Paul wrote, by inspiration, that Jesus was born "of a woman." He did not say that she was a perpetual virgin or that Christ had sex with her. I'm at a loss to see how Paul stating that Mary was a woman (I think the point is she was human, flesh) give dogmatic documentation that Mary was a perpetual virgin? Not only so, but I fail to see any remote connection. I was born of a woman, too - that doesn't dogmatically substantiate that my mother is a perpetual virgin, isn't that obvious?
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Let's look at Matt 1:25, the word "until" in Matt 1:25 is not used to imply that Joseph and Mary had sexual relations after Jesus was born. Rather, the meaning of the passages is simply to make clear that Joseph was not the father of the Christ Child ---that, even though he took her as his wife, Joseph had no relations with her between the time that he took her into his home and the time that the Child was born. Here, you have to remember that the Virgin Birth was something new and unusal (and of course hard to believe) for Matthew's original readers. So, Matthew merely wants to make clear that Joseph could not be the Child's biological father. The passage is not concerned with the subsequent married life of Joseph and Mary or how they lived together, whether in chastity or not. Rather, the focus is on the Virgin Birth itself, and Matthew is defending its miraculous integrity. And the early Church fathers ---native speakers of Biblical Greek ---understood the passage in this way. For example, St. John Chrysostom writes:
" 'And when he had taken her, he knew her not, until she had brought forth
her first-born Son.' He hath here used the word 'until,' not that you should
suspect that afterwards he 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, does he use the word 'until'? Because it is usual in Scripture often
to do this, and to use this expression without reference to limited times.
For so, with respect to the ark likewise it is said, 'the raven returned not
until the earth was dried up.' And yet it did not return even after that
time. And when speaking also of God, the Scripture says, 'From age until age
Thou art,' not as if fixing limits in this case. ...Thus, what it was
necessary for you to learn of Him, He Himself has said: that the Virgin was
untouched by man until the Birth, but that which both was seen to be a
consequence of the former statement, and was acknowledged, this in its turn
He leaves for thee to perceive; namely, that not even after this, she having
to become a mother, and having been counted worthy of a new sort of travail,
and a child-bearing so strange, could that righteous man ever have endured to
know her. For if he had know her, and had kept her in the place of a wife,
how is it that our Lord commits her, as unprotected, having no one, to His
disciple, and commands him to take her into his home? How then, one may say,
are James and the others called His brethren? In the same kind of way that
Joseph himself was supposed to be husband of Mary. For many were the veils
provided, that the birth, being such as it was, be for a time screened.
Wherefore, even John so called them, saying, 'For neither did His brethren
believe in Him.' " ---St. John Chrysostom, On the Gospel of Matthew V:5 (370
A.D.).
Likewise, even the original Protestants understood Matt 1:25 this way, preserving their belief in Mary's perpetual virginity. For example, the Protestant reformer John Calvin writes ...
"There have been certain folk who have wished to suggest that from this
passage [Matt 1:25] that the Virgin Mary had other children than the Son of
God, and that Joseph then dwelt with her later; but what folly this is! For
the gospel writer did not wish to record what happened afterwards; he simply
wished to make clear Joseph's obedience and to show also that Joseph had been
well and truly assured that it was God who had sent His angel to Mary. He had
therefore never dwelt with her nor had he shared her company...And besides
this, Our Lord Jesus Christ is called the first-born. This is not because
there was a second or a third, but because the gospel writer is paying regard
to the precedence. Scripture speaks thus of naming the first-born whether or
not there was any question of the second." (Sermon on Matthew 1:22-25,
published 1562.)
So, those people today (in modern times) who go around saying that Matt 1:25 "proves" that Mary and Joseph lived as a normal married couple are unfaithful to both the Catholic and the traditional Protestant understanding of the passage.
As for Joseph and Mary merely being "betrothed," but at the same time calling each other "husband" and "wife," and Joseph having planned to "divorce" her, .... Here, you must remember that Joseph and Mary were Jews; and they were married according to ancient Jewish custom. In that ancient custom, the woman was literally a piece of propety that was more or less "sold" to the groom by her parents. The first step in this "transaction" was that the groom would sign a marriage agreement with the bride's parents. At that point, she technically belonged to him, and so was referred to as his "wife" ...and sometimes as his "virgin" (see 1 Corinth 7:36-38). However, the marriage contract was not completed at this time. Rather, according to custom, the groom would then return to his own home town (his own father's house) and "prepare a place" for them to live. That is, he would build an extension onto the family home for them to live in. This is the imagery that Jesus evokes when He says (speaking of Heaven), "In my Father's house, there are many mansions; I go to prepare a place for you." Jesus is speaking as the Bridegroom, with the Church as His Bride (see Ephes 5:25-32). So, after signing the contract with Mary's parents, Joseph would have gone to "prepare a place" for them. This was the betrothal period. Mary was already his possession: his wife. But, he had not yet formally claimed her. And, it was during this time that she was found to be pregnant by the Holy Spirit. Not knowing this, Joseph was planning to "divorce" her, which, in the context of the Jewish custom, merely meant that he wanted to dissolve the marriage contract and give her back legally to her parents. But, after being told of God's plan in a dream, he fulfilled the marriage ceremony and took her into his own home. And it is in THIS context that Matt 1:25 says that he had no relations with her "until" the Child was born ...meaning that, even though he fufilled the marriage contract, which would normally have included consummating the marriage with sexual intercourse, he did not do this. Rather, she was legally his wife even before the Child was born ...which is what the "until" really refers to.
Mark Bonoco really helped me to understand this part of my Catholic faith.