To Jews in Jesus' time, what did "the Son of Man" mean?

Question

Jesus quite frequently refers to himself as "the son of man," or we could say "the Son of Man". It is recorded 73 times in the Gospels.

When Jews of the time heard this, would this be understood as a title? ("The Son of Man") How would the 'the' operate here, as opposed to 'a son of man'?

It seems clear it's not synonymous with being the Christ, as shown in Matthew 16:13-17.

"When Jesus came to the region of Caesarea Philippi, He questioned His disciples: “Who do people say the Son of Man is?” 14 They replied, “Some say John the Baptist; others say Elijah; and still others, Jeremiah or one of the prophets.” 15 “But what about you?” Jesus asked. “Who do you say I am?” 16 Simon Peter answered, “You are the Christ, the Son of the living God.” 17 Jesus replied, “Blessed are you, Simon son of Jonah! For this was not revealed to you by flesh and blood, but by My Father in heaven.""

Was Jesus' term 'the son of man' just a nickname by which the disciples understood Jesus was referring to himself? Or did it have a broader cultural meaning, and indicated he was assuming a role short of Messiah but distinguished from other people?

Answer 1

To the Jews at the Time of Christ A lot of answers here have dealt with the definition of "Son of Man," and its etymology. Some have not discerned the difference between the terms in Ezekiel (bar adam) and the one phrase in Daniel (bar enosh). They have lost sight of the posted question at hand. At the time of Christ, what did it mean?.

It is a well-known fact that some words change meaning or just nuances over time. Changes in usage occur over decades or centuries. An example in Jewish vernacular is the ancient phrase for "save now!" Hosanna It is found in Psalms 118:25; and simply was a plea for help. But by the time this word was used in the time of Jesus by the Jews if merely meant an exclamation of praise. And it was used as such by the crowds greeting Jesus grand entry into Jerusalem. (Matthew21:9, 15)

Son of Man So how was this phrase found in Daniel 7:13-14 used at the time of Jesus? The answer is found in several Jewish writings pointed out by the scholar, E.B. Pusey in his commentary on Daniel (pg. 404): The Son of Man is the Messiah.

Zohar;Parasha Toledoth col. 338. in Eisenm. Entd. Jud.ii.756; Rashi. This is Messiah our righteousness (Saadia, comparing with it Ps. cx.1, who shall come into the Presence of God Ibn Yech. adds....Martini Pug. Fid. P.ii.i.13. f. 352, quotes from him (i.e. Aben Ezra): "R. Yeshuah said thatthis (Who was) like the Son of Man, is the Messiah and the saying is right. Add the Tseror Hammor (Mart. p. 214), the Nidrash Tillim, on Ps. ii.2 comparing Ps. cx (Mart. f. 423)...See also Bereshith R. on Gen. xxviii.10, etc.

This phrase, Son of Man, is used in ancient Jewish literature as a title for Messiah (See book of Enoch;Sanhedrin 1:98; Zohar).

The Clouded One Furthermore, The Messiah was also known as the Clouded One. (Anini). "One of the most familiar names of the Messiah was Anini--He who cometh in the Clouds of Heaven. (Edersheim, Life and Times, Vol. I, p, 179.) (Compare Jesus's use of clouds, Matt. 24:30, Mk. 13:26, Matt. 26:63-4, Mk 14:62) (Clouds are also employed in 1 Thess. 4:17, Rev.1:7, 14:14).

There is no doubt that Jesus's use of this phrase 83 times was His applying the rabbinical idea of the long-awaited Messiah to Himself. And at times, the rabbis and priests realized this, to their chagrin and envy! The short answer to the posted question is that At the time of Christ, the rabbis considered the Son of Man to be the Messiah's title.

I saw in the night visions, and behold, one like the Son of Man came with the clouds of heaven, and came to the Ancient of Days...And there was given Him dominion, and glory, and a kingdom, that all people, nations, and languages should serve Him
His dominion is an everlasting dominion which shall not pass away, and His kingdom that which shall not be destroyed (Daniel 7:13-14)

And Jesus came and spoke unto them, saying, "All power is given unto Me in heaven and in earth! Go ye therefore, and teach all nations..." (Matthew 28:18-19)

Answer 2

"Son of man" is a frequent phrase on the OT, especially Ezekiel, (eg, 2:6, 11:15, 12:27, 13:2, 20:3, 21:19, 22;18, 24:2, 28:2, 30:21, 32:18, 24, 33:2, 12, 20, 34:2, 36:1, 37:16, 38:2, 39:17, 40:4, 43:7, 45:5, etc.) See also Job 25:6, Ps 8:4, 80:17, 144:3, Isa 56:2, etc. The phrase also occurs in the plural, "sons of men".

In all these, it simply means, "a mortal man/human" or similar.

The obvious exception to this is the occurrence in Dan 7:13 because it is alluded to in the NT:

Dan 7:13 - “I kept looking in the night visions, And behold, with the clouds of heaven One like a son of man was coming, And He came up to the Ancient of Days And was presented before Him.

Commenting on this passage, Ellicott observes:

(13) The Son of man.—Hence our Saviour adopts the title which designates Him as Judge (Matthew 24:27, &c.). The title implies one descended from man; but as this Person is spoken of as being “like” one of human descent, it follows that He was not merely a man. The early Jewish and Christian interpretations that this is the Messiah are confirmed by our Saviour’s solemn appropriation of the title to Himself (Matthew 24:30). In this verse the judgment is supposed to have already taken place upon earth, and the Son of man comes in the clouds to claim His kingdom.

The Cambridge Commentary is also useful:

with the clouds of heaven in superhuman majesty and state. The passage is the source of the expression in Mark 14:62 (Matthew 26:64 ‘on’); Revelation 1:7, ‘behold, he cometh with the clouds:’ cf. Matthew 24:30 (‘on’) = Mark 13:26 (‘in’) = Luke 21:27 (‘in’); and Revelation 14:14 (‘one sitting on a cloud, like unto a son of man’), 15, 16.

Significantly, Jesus is the only person qualified to take both titles:

• "Son of Man" because He was biologically descended from humans because He was the Son of Mary
• "Son God" because He was also (biologically??) descended from God as per Luke 1:35 which encapsulates both -

The angel replied, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the Holy One to be born will be called the Son of God.

Jews well versed in Scripture would have been familiar with the Messianic prophecy in Dan 7:13 which also provided another source of wonder for them - How could this humble carpenter be Messiah and King of Israel, the "Son of Man" prophesied by Daniel?? Little wonder they wanted to kill Him.

Son of Man in the NT

In the NT, the title for Jesus, "Son of Man" occurs 86 times, 82 of these in the Gospels such as Matt 8:20, 9:6, 10:23, 11:19, 12:8, 32, 40, etc, and almost always in the mouth of Jesus. Indeed, it was (based on frequency) Jesus favorite title for Himself - in the Gospels the title is used only in the mouth of Jesus.

Answer 3

It looks like the Jews at Jesus time thought the Son of man was someone who had lived before and came back to life. Not sure if they understood that the son of man was also the Christ.

Who do people say the Son of Man is?” 14 They replied, “Some say John the Baptist; others say Elijah; and still others, Jeremiah or one of the prophets.”

“This is John the Baptist. He has been raised from the dead; that is why these miraculous powers are at work in him.”Mathew 14:2

Jesus asked Peter who he thought the son of man was.

“Who do you say I am?” 16 Simon Peter answered, “You are the Christ, the Son of the living God.” 17 Jesus replied, “Blessed are you, Simon son of Jonah! For this was not revealed to you by flesh and blood, but by My Father in heaven.""

This was a a revelation to Peter first as to who is the son of man was. It was Jesus who was also the Christ.

It is confirmed that the Christ of God is also the Son of man.

and it came to pass, as he was alone praying, his disciples also were with him: and he asked them, saying: Whom do the people say that I am? 19But they answered and said: John the Baptist; but some say Elias: and others say that one of the former prophets is risen again. 20And he said to them: But whom do you say that I am? Simon Peter answering, said: The Christ of God. 21But he strictly charging them, commanded they should tell this to no man. 22Saying: The Son of man must suffer many things and be rejected by the ancients and chief priests and scribes and be killed and the third day rise again. Luke 9:18:21

This revelation that was given to Peter, was given to the world as to who is the Son of man is as well as the Christ.

Answer 4

In general, the Hebrew phrase "son of man" can mean a son of mankind, a human, or an earthing son.

The topic "Son of Man" in the Insight on the Scriptures explains in more detail:

In Hebrew this is mainly a translation of the expression ben-ʼa·dhamʹ. Instead of referring to the person, Adam, ʼa·dhamʹ is here used generically for “mankind” so that the expression ben-ʼa·dhamʹ means, in essence, “a son of mankind, a human, an earthling son.” (Ps 80:17; 146:3; Jer 49:18, 33) The phrase is often employed in parallel with other Hebrew terms for “man,” namely, ʼish, meaning “a male person” (compare Nu 23:19; Job 35:8; Jer 50:40) and ʼenohshʹ, “a mortal man.” (Compare Ps 8:4; Isa 51:12; 56:2.) At Psalm 144:3 the “son of mortal man” is ben-ʼenohshʹ, while the Aramaic equivalent (bar ʼenashʹ) appears at Daniel 7:13.

. . .

In the Hebrew Scriptures the most frequent occurrence of the expression is in the book of Ezekiel, where over 90 times God addresses the prophet as “son of man.” (Eze 2:1, 3, 6, 8) The designation as so used apparently serves to emphasize that the prophet is simply an earthling, thus heightening the contrast between the human spokesman and the Source of his message, the Most High God. The same designation is applied to the prophet Daniel at Daniel 8:17.

As to Jesus Christ using the phrase "the Son of Man", the article points out that Jesus was distinguishing himself as a flesh and blood being as opposed to a materialized angel:

In the Gospel accounts the expression is found nearly 80 times, applying in every case to Jesus Christ, being used by him to refer to himself. (Mt 8:20; 9:6; 10:23) The occurrences outside the Gospel accounts are at Acts 7:56; Hebrews 2:6; and Revelation 1:13; 14:14.

Jesus’ application of this expression to himself clearly showed that God’s Son was now indeed a human, having ‘become flesh’ (Joh 1:14), having ‘come to be out of a woman’ through his conception and birth to the Jewish virgin Mary. (Ga 4:4; Lu 1:34-36) Hence he had not simply materialized a human body as angels had previously done; he was not an incarnation but was actually a ‘son of mankind’ through his human mother.​—Compare 1Jo 4:2, 3; 2Jo 7; see FLESH.

Additionally, Jesus' usage of the phrase "Son of Man" also identified him as the one who could redeem mankind from sin and death:

The designation “Son of man,” therefore, also serves to identify Jesus Christ as the great Kinsman of mankind, having the power to redeem them from bondage to sin and death, as well as to identify him as the great Avenger of blood.​—Le 25:48, 49; Nu 35:1-29; see AVENGER OF BLOOD; RANSOM; REPURCHASE, REPURCHASER.

In one instance, Jesus identified himself as the Messiah by the usage of the phrase "Son of man". In John 12:23-36, Jesus refers to himself as the "Son of man". After this Jehovah God speaks from heaven. Jesus then speaks about how he must be "lifted up". At this point, the crowd is confused about what Jesus is saying:

Then the crowd answered him: “We heard from the Law that the Christ remains forever. How can you say that the Son of man must be lifted up? Who is this Son of man?” (John 12:34)

So by using the phrase "son of man", Jesus not only meant that he was a flesh and blood human, but also that he identified himself as the Messiah and the Redeemer of all mankind.

[All scripture quotations from the New World Translation of the Holy Scriptures (Study Edition)]

Answer 5

The Son of man was a nickname of the Messiah, well known to the learned Jews. All the prophecies used in the NT to allude to his being the Messiah, the Son of God, are found in the rabbinic literature or commentaries which attest the contemporary view of the Jews.

Michael Brown writes in Answering Jewish Objections to Jesus, vol 2, objection 3.3 God doesn't have a son:

Psalm 2 in the Tanakh in light of a homiletical Rabbinic commentary called Midrash Tehillim. The midrash is addressing the words, “I will declare the decree. The LORD said to me, ‘You are my son; today I have begotten you.’” Which decree, the rabbis ask, is being referred to here? First, it is answered, the text refers to “the decree of the Torah,” Exodus 4:22, where God calls Israel his firstborn son. In other words, just as Israel was God’s son, so also the king was God’s son. Next, it refers to “the decree of the Prophets,” citing Isaiah 52:13 (“Behold, my servant will act wisely”) and Isaiah 42:1 (“Here is my servant, whom I uphold, my chosen one in whom I delight”). Now, what is interesting here is that neither of these verses makes reference to the term son, yet they are among the most famous Messianic prophecies in the entire Bible, often pointed to by Christians with ultimate reference to Jesus. And the midrash ties them in with the king being called God’s son in Psalm 2:7!

Next, the rabbis point to “the decree of the Writings” (i.e., the remainder of the Tanakh), citing Psalm 110:1, “The LORD said to my lord, ‘Sit at my right hand,’” a verse quoted by Jesus himself to demonstrate that as Messiah, he was more than just David’s son, since David in Psalm 110 called him “my lord” (see Matt. 22:42–45). And all this is given in explanation of “the decree” proclaiming the Davidic king as God’s son. But it gets even better.

The final verse cited is Daniel 7:13: “In my vision at night I looked, and there before me was one like a son of man, coming with the clouds of heaven.” Thus, in light of this Rabbinic compilation of Scripture, the exalted figure coming in the clouds of heaven is none other than the Davidic king, the Son of God! (Remember this is Rabbinic midrash not New Testament commentary.) From a Messianic standpoint, this verse in Daniel is of critical importance.

Now, let’s put this all together: According to this Midrash, the justification for calling the king the son of God is based on: (1) God calling Israel his firstborn son; (2) prophecies from Isaiah referring to the faithful servant of the Lord, clearly Messianic references; and (3) a royal psalm in which God says to the king, “Sit at my right hand,” and the glorious “son of man” prophecy from Daniel. If I didn’t read this myself in the Hebrew Midrash Tehillim, I would have thought that a Messianic Jew put these verses together. They are some of the most common texts that we quote, all with reference to Jesus the Messiah. And here the rabbis tie them in with the Davidic king as son of God. In fact, Rabbi Yudan states explicitly that the words “you are my son” refer to the Messiah.

There were a number of Davidic kings in our history, some of whom were great, like David, Solomon, Hezekiah, and Josiah, and each of whom would have been called “God’s son.” But none of them sat down at God’s right hand (Psalm 110), none of them were (or are) worshiped and adored by people of every nation and tongue (Daniel 7), and only Yeshua, who called himself both “Son of man” and “Son of God,” will return in the clouds of heaven (again, Daniel 7). He fulfills that which was prophetically spoken of the Davidic king, the anointed (mashiach) of the Lord, in the Prophets and Psalms.

Answer 6

“Human”. A more literal translation, by the way, would be “Son [descendant] of Adam” (which C.S. Lewis used). “Son of Man” is iffy; ‘man’ is usually ‘בן-אדם’ or ‘איש’, depending on whim of the speaker (although the former is less likely to be specifically male); ‘אדם’ is rather more polysemous than those, possibly meaning “red” or “redness” (although it's a defective spelling for those) as well as “Adam” or “human”.

Also, the main requirement for the Messiah is that they bring peace. (Isaiah 2:4, among others.) As there is still clearly war in the world, they have not yet come.

Dottard says

Jews well versed in Scripture would have been familiar with the Messianic prophecy in Dan 7:13 which also provided another source of wonder for them - How could this humble carpenter be Messiah and King of Israel, the "Son of Man" prophesied by Daniel?? Little wonder they wanted to kill Him.

I should point out that 7:14 says “שלטנה שלטן עלם די-לא יעדה ומלכותה די-לא תתחבל”, which roughly translates to “His dominion is a dominion of the world, that will not end, and his kingdom will not be destroyed” (my Aramaic isn't that good, but except for ‘די’ (‘that’) it's essentially the same as Hebrew). The most likely thought someone would have had about someone claiming to be the Messiah would have been “This guy's a nut. Maybe he is, maybe he isn't. It's too early to tell.” (Except in Aramaic, of course.) After all, one who doesn't bring peace can't be the Messiah, and that hadn't happened yet. The chief reason for anger would be that he completely messed up the absolutely necessary¹ work of the money-changers and made it so it was impossible to tell whose money was whose.

¹Because you can't sacrifice an animal with a blemish, so you sell the animal at home, head to Jerusalem, and there trade your coins so you don't have any with pagan gods on them; then you buy unblemished animals for sacrifice. The best possible spin on that story is that he got really mad at one ממזר who was shortchanging people and specifically toppled his table, and the tale got exaggerated in the telling.

Answer 7

To Jewish audiences in Jesus’ time, the term “Son of Man” carried rich, multi-layered meanings that intertwined both the frailty of humanity and prophetic authority. Let’s explore its depth by examining its roots in the Hebrew Bible, the Septuagint, and other Jewish texts, with a focus on the humanity of the Messiah and the title’s prophetic implications.

1. Humanity and Vulnerability: The term "son of man" appears in passages like Numbers 23:19 and Judith 8:16, where God is contrasted against humanity, emphasizing that He is not susceptible to human failings or fickleness. In these contexts, "son of man" (υἱὸς ἀνθρώπου) signifies human limitations, a recurring theme that underscores humanity’s impermanence and tendency to falter, as Jesus noted in statements like “the flesh is weak” (Matt. 26:41). In Job 25:6, man is called a “worm,” further stressing this vulnerability.

2. Messianic Hope and Divine Appointment: In texts like Psalm 80:17, the phrase points to a divinely appointed figure: “Let your hand be on the man of your right hand, on the son of man whom you made strong for yourself.” Here, the Son of Man represents a chosen leader empowered by God, perhaps a precursor to the messianic hope seen in later Jewish thought.

3. Mortal Nature: Jewish wisdom literature, such as Sirach 17:30, reflects the notion that “the son of man is not immortal,” underscoring the belief in human mortality. This association presents the Son of Man as one who shares in humanity’s transitory nature, yet is called by God for a greater purpose.

Prophetic Role in Ezekiel: The prophet Ezekiel is frequently addressed as “son of man” (Ezek. 2:1, 6:2) in the Septuagint, emphasizing his role as a human intermediary conveying divine messages to Israel. In this prophetic role, the title highlights humility, frailty, and accountability, traits that link the Son of Man with themes of obedience and service.

4. Apocalyptic Vision in Daniel: The most striking instance of the term comes from Daniel 7:13, where “one like a son of man” is seen coming “with the clouds of heaven” to the “Ancient of Days.” This figure is granted authority, dominion, and eternal kingship, which became central to Jewish messianic expectations. The imagery suggests a figure both humble and exalted, human yet somehow sharing in divine authority—a paradox later echoed in New Testament Christology.

5. Gospel and New Testament Context: In the Gospels, Jesus often refers to himself as the "Son of Man," embracing both the humility of human frailty and the authority to judge (John 5:27). He adopts this title to convey his connection to humanity’s weakness, yet also his unique role as the divinely appointed judge and redeemer, an idea that resonated with the Jewish audience familiar with Daniel's vision.

6. Apocalyptic Revelation: The Book of Revelation also uses this term in a highly exalted sense. Describing the vision of “one like a son of man” clothed in divine attire (Rev. 1:13) or seated on a white cloud with a crown and sickle (Rev. 14:14), it emphasizes the eschatological role of the Son of Man as an ultimate judge and redeemer at the end of time.

7. Interpretations in Jewish Pseudepigrapha and Philo:

OPG TS1 5:3 καὶ εἶπον αὐτῷ• Οὕτως τετιμωρημένος ἀποκρίνῃ; ὁ δὲ τῷ αὐτῷ βλέμματι προσχὼν εἶπέ μοι• Πῶς ἔχω σοι ἀποκριθῆναι; σὺ μὲν υἱὸς ἀνθρώπου εἶ, κἀγὼ ἀγγέλου, καὶ διὰ θυγατρὸς ἀνθρώπου ἐγεννήθην, ὥστε οὐδὲν ὑπερήφανον ῥῆμα οὐρανίου γένους πρὸς γηγενῆ.

And they said to him, "Do you respond, thus punished?" But he, with the same gaze fixed upon me, said, "How can I respond to you? You are a son of man, and I am of an angel, and I was begotten through a daughter of man, so that there is no arrogant word from a heavenly being toward one born of earth."

PHI Mos. 1:283 ὁ δὲ μονωθεὶς ἐξαίφνης θεοφορεῖται καὶ μηδὲν συνιείς, ὥσπερ μετανισταμένου τοῦ λογισμοῦ, τὰ ὑποβαλλόμενα ἐξελάλει προφητεύων τάδε• "ἀναστὰς ἄκουε, βασιλεῦ, τὰ ὦτα ἐπουρίσας. οὐχ ὡς ἄνθρωπος ὁ θεὸς διαψευσθῆναι δύναται οὐδ᾽ ὡς υἱὸς ἀνθρώπου μετανοεῖ καὶ ἅπαξ εἰπὼν οὐκ ἐμμένει. φθέγξεται τὸ παράπαν οὐδέν, ὃ μὴ τελειωθήσεται βεβαίως, ἐπεὶ ὁ λόγος ἔργον ἐστὶν αὐτῷ. παρελήφθην δ᾽ ἐπ᾽ εὐλογίαις, οὐ κατάραις, ἐγώ.

But when he was left alone, he was suddenly filled with divine inspiration and, understanding nothing, as if his reasoning had been displaced, he uttered the things being suggested, prophesying as follows: "Arise, listen, O king, lifting your ears on high. God is not like a man, able to be deceived, nor like a son of man to repent, nor does He fail to keep His word once spoken. He will by no means utter anything that will not certainly be fulfilled, for His word is His deed. And I have been summoned for blessings, not curses."

Jewish works like the Pseudepigrapha further illustrate the Son of Man as embodying humanity’s relationship with the divine, while Philo of Alexandria views the term in philosophical terms, representing the Logos as a mediator between God and humanity, bridging divine reason with human frailty.

Thus, for Jews of Jesus' time, the Son of Man held complex meanings that spanned human vulnerability, prophetic duty, and messianic expectation. Jesus’ self-identification with this title may have appeared paradoxical, as he claimed both solidarity with human weakness and an elevated, divine mission, echoing the vision of Daniel while aligning with Ezekiel’s prophetic humility.

Answer 8

'Son of Man' = the pre-eminent son of Adam; though He was not Adamic nor from Adam. Rather, as the offset for Adam, He would be the Ransom(er) [1 Tim. 2: 5], the only one capable of such a redeeming sacrifice, and thus He was the best among 'men'.

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Jesus identified Himself as ʻthe Son of Godʼ (Matt. 4:3). He is occasionally called by others and Himself, ʻthe Son of Davidʼ, following the Jewish tradition of asserting oneʼs cultural or religious lineage (Matt. 15:22). And it was common for a son to be linked not only with his father, or a trade, but also with a trait of character, as with James and John, the fleshly sons of Zebedee, but styled by Jesus ʻSons of Thunderʼ (Mark 3:17).

He also referred to Himself as ʻthe Son of Man [anthropos]ʼ. Not that He was of ordinary human descent; the Scriptures declare He was not (John 1:14). At no time did Jesus refer to Adam as His father, though He was nonetheless the pre-eminent representative of the human family. Prospectively He was heir to headship over the human family, finally purchasing this right by His sacrificial death (Rom. 14:9). Thus He became the new owner and (putative) progenitor of the human race in place of Adam, who had forfeited his right to rule.

The title, Son of Man, applied to Jesus before and after His resurrection. See Mark 13:26, ʻthe Son of Man . . . coming in clouds with great power and gloryʼ; Luke 18:8, ʻwhen the Son of Man comes . . .ʼ). See also Matt. 16:13-16, in which ʻthe son of [the] manʼ; v.13) is regarded by Peter as synonymous with ʻthe Son of . . . [the] Godʼ; v.16).

Luke’s introduction of Jesus at 30 – now a full ‘man’ under the Law – and his genealogy of Joseph (Luke 3:23-38) traces back to Adam, the only other ‘[perfect, sinless] man’ and ‘[son of] God’ (v. 38). One may, perhaps, read into vs. 23 and 38 a hint that Jesus thus supplants Adam as uniting in Himself the son ‘of [the] God’ and ‘[the] son of [the] Man’; I don’t know. Nonetheless, Paul’s language in Rom. 5:14 seems unambiguous as to their being equivalent.

Answer 9

Could it be that Jesus asks the question "Who do people say the Son of Man is?" just to get the disciples thinking about the meaning of that expression so that his follow up question "And who do you say I am?" leads to Peter's ah ha moment realizing the connection between the term Son of Man and Jesus, himself?

Answer 10

In his day, people called Jesus rabbi, teacher, master, lord, even son of God. That he called himself son of man deserves our careful consideration. It obviously held special meaning for him, but what?

At the baptism of Jesus, the heavens opened, symbolizing that the traditional separation between God and man was suspended. Jesus had a close encounter with God where God proclaimed Jesus his beloved son, and the spirit - God's spirit - entered into Jesus. Then the spirit took him into the wilderness. (Mt 3:16-4:1) )

Ezekiel too had his close encounter with God, multiple times. This lengthy book of prophecy had the thread running through it, of one man's experience of being in the presence of God. God repeatedly called Ezekiel son of man. And, the spirit was always lifting him up and taking him here and there. (Ezekiel 2:1-2, and numerous others)

See also Daniel 8:17, for another, similar use of "son of man."

I think it is safe to say that Jesus' baptism wasn't the only time he found himself in the presence of God. Perhaps in those times when he was in the presence, God also called Jesus son of man, as God did with Ezekiel. Or, perhaps Jesus just saw a parallel between his God-encounters and those of Ezekiel, and adopted the usage of the term. In any case, his self-designation as son of man signified in him a transformed inner state, so that he would proclaim, "I and the Father are one." (John 10:30)