Matthew 1:18

18.Now the birth of Jesus Christ Matthew does not as yet relate the place or manner of Christ’s birth, but the way in which his heavenly generation was made known to Joseph. First, he says that Mary was found to be with child by the Holy Spirit Not that this secret work of God was generally known: but the historian mixes up, with the knowledge of men, (97) 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 So far as respects conjugal fidelity, from the time that 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 of the 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.)

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