Why did Jesus call the paralyzed man "son" in Mark 2:5?

Question

The paralyzed man was carried by four men.

Mark 2:3-5 Some men came, bringing to him a paralyzed man, carried by four of them. Since they could not get him to Jesus because of the crowd, they made an opening in the roof above Jesus by digging through it and then lowered the mat the man was lying on. When Jesus saw their faith, he said to the paralyzed man, “Son, your sins are forgiven.”

Later, Jesus refers to himself as Son of Man in verse 10:

But I want you to know that the Son of Man has authority on earth to forgive sins.

Is there a relationship between "Son of Man" and "son"? Why did he call a grown man son?

Answer 1

And, behold, they brought to him a man sick of the palsy, lying on a bed: and Jesus seeing their faith said unto the sick of the palsy; Son, be of good cheer; thy sins be forgiven thee. (Matthew 9:2, KJV)

When Jesus saw their faith, he said unto the sick of the palsy, Son, thy sins be forgiven thee. (Mark 2:5, KJV)

Jesus used terms of familiarity and endearment to address people because of his great love toward them which he was unable to conceal. More than this, as the poor sufferers heard such affectionate terms used to address them, it gave them hope and comfort in knowing that they were accepted of him, their Savior.

Two particular cases of this are on record: the palsied man of this question, and the woman who had the issue of blood for so many years--recorded in three of the gospels.

But Jesus turned him about, and when he saw her, he said, Daughter, be of good comfort; thy faith hath made thee whole. And the woman was made whole from that hour. (Matthew 9:22, KJV)

And he said unto her, Daughter, thy faith hath made thee whole; go in peace, and be whole of thy plague. (Mark 5:34, KJV)

And he said unto her, Daughter, be of good comfort: thy faith hath made thee whole; go in peace. (Luke 8:48, KJV)

But Jesus also pitied those women who mourned his fate as he passed them on the way to Calvary.

But Jesus turning unto them said, Daughters of Jerusalem, weep not for me, but weep for yourselves, and for your children. (Luke 23:28, KJV)

Jesus began his ministry at the age of 30, and ministered only three and a half years, being crucified at the age of 33. It is quite probable that when he said "Son" and "Daughter" to these two afflicted ones, they were actually older than he was.

We know the woman had had her issue of blood for 12 years. Assuming that she had begun to have the issue while only a teenager, she would still have been nearly the same age as Jesus--certainly not young enough to be his daughter. We also know that the palsied man had been in his paralyzed condition for many years, though we are not told exactly how many. Again, he cannot have been much younger than Jesus, if he was at all.

Conclusion

Jesus did not use these terms merely to make himself appear to have a superior status--he used them with tender affection, demonstrating his love and acceptance of them. And, of course, Jesus was speaking on behalf of the Father, his Father and their heavenly Father, who loved, accepted, and healed them.

Answer 2

And when Jesus saw their faith, he said to the paralytic, “Son, your sins are forgiven.”
(Mark 2:5) [ESV]

καὶ ἰδὼν ὁ Ἰησοῦς τὴν πίστιν αὐτῶν λέγει τῷ παραλυτικῷ τέκνον ἀφίενταί σου αἱ ἁμαρτίαι

Jesus called him "τέκνον" which is most frequently translated as child, but in this case the use is considered to be one of familiar address:

❸ one who is dear to another; but without genetic relationship and without distinction in age, child a. in the voc. gener. as a form of familiar address my child, my son (Herodian 1, 6, 4; ParJer 5:30; Achilles Tat. 8, 4, 3. Directed to fully grown persons, Vi Aesopi G 62 P., where a peasant addresses Aesop in this way) Mt 9:2; Mk 2:5¹

There are other possibilities. It is also used as as a Hebraic expression for inhabitants of a city:

“O Jerusalem, Jerusalem, the city that kills the prophets and stones those who are sent to it! How often would I have gathered your children together as a hen gathers her brood under her wings, and you were not willing! (Matthew 23:37)

Ἰερουσαλὴμ Ἰερουσαλήμ, ἡ ἀποκτείνουσα τοὺς προφήτας καὶ λιθοβολοῦσα τοὺς ἀπεσταλμένους πρὸς αὐτήν— ποσάκις ἠθέλησα ἐπισυναγαγεῖν τὰ τέκνα σου, ὃν τρόπον ὄρνις ἐπισυνάγει τὰ νοσσία αὐτῆς ὑπὸ τὰς πτέρυγας, καὶ οὐκ ἠθελήσατε

The location is specifically in Capernaum, so it is possible Jesus is using the term in that sense. He may also be using the term in the sense John will later explain:

But to all who did receive him, who believed in his name, he gave the right to become children of God (John 1:12)

ὅσοι δὲ ἔλαβον αὐτόν, ἔδωκεν αὐτοῖς ἐξουσίαν τέκνα θεοῦ γενέσθαι, τοῖς πιστεύουσιν εἰς τὸ ὄνομα αὐτοῦ

The man's own faith is never mentioned, only that of his friends. However, if he were to believe in Jesus' name, he would have the right to become a τέκνον of God. This may be the primary reason for calling a man "child." In other words, Jesus used it as a familiar form of address and the man's experience will cause him to become a believer and a child of God.

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1. Fredrick William Danker, A Greek-English Lexicon of the New Testament and Other Early Christian Literature, The University Chicago Press, 2000, p. 994