John Calvin Commentary Matthew 1:18

"Now the birth of Jesus Christ was on this wise: When his mother Mary had been betrothed to Joseph, before they came together she was found with child of the Holy Spirit." — Matthew 1:18 (ASV)

Now the birth of Jesus Christ. Matthew does not yet describe the place or manner of Christ’s birth, but the way in which his heavenly generation was revealed to Joseph.

First, he says that Mary was found to be with child by the Holy Spirit. It was not that this secret work of God was generally known; rather, the historian combines what was known by people⁹⁷ with the power of the Spirit, which was still unknown.

He points out the time: When she was espoused to Joseph, and before they came together. Regarding conjugal fidelity, from the time a young woman was betrothed to a man, she was regarded by the Jews as his lawful wife.

When a “damsel betrothed to an husband” was convicted of being unchaste, the law condemned both guilty parties as adulterers:

“the damsel, because she cried not, being in the city;
and the man, because he hath humbled his neighbor’s wife,”
(Deuteronomy 22:23–24)

The phrase used by the Evangelist, before they came together, is either a modest term for conjugal intercourse, or simply means, “before they came to dwell together as husband and wife, and to make one home and family.” Thus, the meaning will be, that the virgin had not yet been delivered by her parents into the hands of her husband, but still remained under their roof.

⁹⁷ (“Qui voyoyent bien par signes externes que Marie estoit enceinte.”) —(“Who saw well by outward marks that Mary was pregnant.”).”) —(“Who saw well by outward marks that Mary was pregnant.”)