but knew her not until she had given birth to a son. And he called his name Jesus.
25. And knew her not This passage afforded the pretext for great disturbances, which were introduced into the Church, at a former period, by Helvidius. The inference he drew from it was, that Mary remained a virgin no longer than till her first birth, and that afterwards she had other children by her husband. Jerome, on the other hand, earnestly and copiously defended Mary’s perpetual virginity.
The mystery of Christ's incarnation is to be adored, not pried into. If we know not the way of the Spirit in the formation of common persons, nor how the bones are formed in the womb of any one that is with child (Ecc 11:5), much less do we know how the blessed Jesus was formed in the womb of the blessed virgin.
Commenting on Matthew 1:18-25
And knew her not,.... Or "but he knew her not", answering to the Hebrew that is, had carnal knowledge of her, or copulation with her, though his wife. The words are an euphemism, or a modest way of expressing the conjugal act, and is a very ancient one, see Gen 4:1 and what has been used in nations and languages.