And knew her not till she had brought forth her firstborn son: and he called his name JESUS.
All Commentaries on Matthew 1:25 Go To Matthew 1
And when Joseph had taken her, “he had no relations with her until she had borne a son.” Matthew has here used the word until not that you should suspect that afterward Joseph did know her but to inform you that before the birth the Virgin was wholly untouched by man. But why then, it may be said, has he used the word until? Because it is common in Scripture that this expression is used without reference to specific, limited times. Here are three examples. First, in the narrative of the ark it was said that “the raven did not return until the earth was dried up,” yet the raven did not return even after that limited time. Second, when discussing God the Scripture says, “You are from everlasting to everlasting,” but there is no implication here that some limit is being fixed—rather the opposite. Third, when preaching the gospel beforehand and saying, “In his days may righteousness flourish, and peace abound, until the moon be no more!” it is not thereby setting a temporal limit to this beautiful part of creation. So then here likewise, it uses the word until to make certain what was before the birth, but as to what follows, it leaves some further inference to be made. So it is necessary to learn what Matthew teaches: that the Virgin was untouched by man until the birth. But the rest is left for you to perceive, both as a consequence of the previous narrative and what was later acknowledged: that not even after having become a mother and having been counted worthy of a new sort of travail and a childbearing so strange, could that righteous man ever have permitted himself to have sexual relations with her. The Gospel of Matthew, Homily