Why is Matthew 1:18 understood as referring to a virgin conception?

Question

Matthew 1:18 (NIV)

This is how the birth of Jesus the Messiah came about[a]: His mother Mary was pledged to be married to Joseph, but before they came together, she was found to be pregnant through the Holy Spirit.

It says Mary became pregnant through the Holy Spirit, but how does one rule-out the involvement of a male in fertilizing the egg? Other miraculous conceptions in the bible are not usually understood as involving a non-sexual conception, so why is a non-sexual conception inferred here?

Answer 1

There are three things that have led people to believe in the virgin birth of Jesus, based on the inspired record in Matt 1:18-25 -

• V18, "before they [Mary and Joseph] came together [= had slept together], Mary was found with a child in the womb out of [= ἐκ] the Holy Spirit
• V19-24 - Joseph then considers this and plans to break the engagement but quietly to minimize the problem on Mary because Joseph knew that he had had no part in the conception
• V25, (BLB) "But he did not know her until she had brought forth a Son, and he called His name Jesus." Other versions are more bunt:

NIV: But he did not consummate their marriage until she gave birth to a son.

NLT: But he did not have sexual relations with her until her son was born.

NASB: but kept her a virgin until she gave birth to a Son

CSB: but did not have sexual relations with her until she gave birth to a son

GNT: But he had no sexual relations with her before she gave birth to her son

Thus, the inspired record in Matthew confirms that Mary had a virgin birth when Jesus was born. The physician, Luke, also confirms that Mary was a virgin in Luke 1:26-35 -

In the sixth month, God sent the angel Gabriel to a town in Galilee called Nazareth, to a virgin pledged in marriage to a man named Joseph, who was of the house of David. And the virgin’s name was Mary. The angel appeared to her and said, “Greetings,b you who are highly favored! The Lord is with you.c”

Mary was greatly troubled at his words and wondered what kind of greeting this might be. So the angel told her, “Do not be afraid, Mary, for you have found favor with God. Behold, you will conceive and give birth to a son, and you are to give Him the name Jesus. He will be great and will be called the Son of the Most High. The Lord God will give Him the throne of His father David, and He will reign over the house of Jacob forever. His kingdom will never end!”

“How can this be,” Mary asked the angel, “since I am a virgin?”

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.

Answer 2

First, the text eliminates the possibility that Joseph’s seed contributed to the conception because it said Mary was found pregnant (lit., “having in her womb”) while she and Joseph were betrothed and before she and Joseph came together (i.e., had intercourse).

Notice the phrase at the end: «ἐκ πνεύματος ἁγίου». The text does not use the prepositions διὰ or ὑπὸ to suggest that the Holy Spirit functioned as an instrumental agent in the conception.¹ Rather, it uses ἐκ. For example, in Rom. 9:10, the apostle Paul wrote the following:²

¹⁰ and not only this, even Rebecca, having conception of one, our father Isaac,

^Ιʹ οὐ μόνον δέ ἀλλὰ καὶ Ῥεβέκκα ἐξ ἑνὸς κοίτην ἔχουσα Ἰσαὰκ τοῦ πατρὸς ἡμῶν·

In Rom. 9:10, ἐξ is referring to the father of the offspring (twins) conceived in Rebecca. Likewise, in Matt. 1:18, ἐξ is referring to the father of the offspring conceived in Mary. For that reason, the child was called the son of God.³

Footnotes

        ^{1 As in the case of God enabling an infertile woman such as the 90-year old Sarah to conceive Isaac with Abraham. Gen. 17:17 cf. Gen. 21:2.
        2 Rom. 9:10 has the word κοίτην, literally “bed.” Most translators agree that it is understood as “intercourse,” but not only that. As a metonymy of the cause for the effect, the author likely means seed or conception. BDAG, κοίτη, 2., b., has a remark on Rom. 9:10: κοίτην ἔχειν ἐξ ἑνός conceive children by one man Ro 9:10. Likewise, in the LXX of Num. 5:20, it has «καὶ ἔδωκέν τις τὴν κοίτην αὐτοῦ ἐν σοὶ»—“and if some man gave you his bed in you.” (Here, κοίτην clearly refers to seed.)
        3 cf. Luke 1:35}

Answer 3

Here is the passage from the ancient Greek translation to which he appeals:

Isaiah 7:14 Brenton(i) 14 Therefore the Lord himself shall give you a sign; behold, a virgin shall conceive in the womb, and shall bring forth a son, and thou shalt call his name Emmanuel.

Matthew has demonstrated repeatedly that he is working from a Greek translation, not from a Hebrew text (though see here). He is determined by hook or crook to have every OT passage (as found in the Greek translation) find a corresponding "fulfillment" in his gospel. For example, "out of Egypt have I called my son" is proffered by Matthew as being "fulfilled" in Joseph's family escaping Herod (something of which his biographers never show any knowledge, and clearly refers to Israel escaping slavery in Egypt). And he has his family moving to Nazareth "fulfilling" the passage:

[Jdg 13:5 KJV] (5) For, lo, thou shalt conceive, and bear a son; and no razor shall come on his head: for the child shall be a Nazarite unto God from the womb: and he shall begin to deliver Israel out of the hand of the Philistines.

[Mat 2:23 KJV] (23) And he came and dwelt in a city called Nazareth: that it might be fulfilled which was spoken by the prophets, He shall be called a Nazarene.

So Matthew contrives all kinds of fictional nonsense to show that Jesus was, in fact, the Messiah, and the fulfillment of ALL prophecy.

Since that is his driving design for his gospel (and the same is true of all the NT), he recasts the "sign" that Isaiah predicted for his current time as referring to the NT times, aka "the Messianic Age":

[Isa 7:16 KJV] (16) For before the child shall know to refuse the evil, and choose the good, the land that thou abhorrest shall be forsaken of both her kings.

[Isa 8:4 KJV] (4) For before the child shall have knowledge to cry, My father, and my mother, the riches of Damascus and the spoil of Samaria shall be taken away before the king of Assyria.