And knew her not till she had brought forth her firstborn son: and he called his name JESUS.
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Helvidius is at much superfluous trouble to make this word "know” refer to carnal knowledge rather than to acquaintance, as though any had ever denied that; or as if the follies to which he replies had ever occurred to any person of common understanding. He then goes on to say, that the adverb, 'until,’ denotes a fixed time when that should take place, which had not taken place before; so that here from the words, “He knew her not until she had brought forth her first-born Son,” it is clear, he says, that after that he did know her. And in proof of this he heaps together many instances from Scripture. To all this we answer, that the word 'until’ is to be understood in two senses in Scripture. And concerning the expression, “knew her not,” he has himself shewn, that it must be referred to carnal knowledge, none doubting that it is often used of acquaintance, as in that, “The child Jesus tarried behind in Jerusalem, and His parents knew not of it.” So here the Evangelist informs us, in that wherein there might have been room for error, that she was not known by her husband until the birth of her Son, that we might thence infer that much less was she known afterwards. Lastly, I would ask, Why then did Joseph abstain at all up to the day of birth? He will surely answer, Because of the Angel’s words, “That which is born in her” He then who gave so much heed to a vision as not to dare to touch his wife, would he, after he had heard the shepherds, seen the Magi, and known so many miracles, dare to approach the temple of God, the seat of the Holy Spirit, the Mother of his Lord?
From the words, “her first-born Son,” some most erroneously suspect that Mary had other sons, saying that first-born can only be said of one that has brethren. But this is the manner of Scripture, to call the first-born not only one who is followed by brethren, but the first-birth of the mother.
For if he only was first-born who was followed by other brethren, then no first-birth could be due to the Priests, till such time as the second birth took place.