You wrote (to Karen):
Every Protestant commentator on Isaiah that I have ever read mentions the difference between the reading of the Hebrew and of the Septuagint on the word "alma" and "bethulah," at Isaiah 7:14. It is not a Catholic point. It would be very weak to support the virgin birth on this verse alone, since the verse, in its context, is not obviously predicting the birth of the Messiah. So "Where do you get the Scriptural sense that she is a virgin...?" The answer is, from other relevant scriptures, and the New testament citation of this one as well. This is the way Protestants recommend that biblical studies be done: take all the relevant statements of scripture, and do not give any of them a meaning that is not justified by its context.Ok, that being said. Where do you get the Scriptural sense that she is a virgin, when the Jewish OT states that she is simply a "young woman". Earlier I illustrataed very different Hebrew words for virgin and young woman. Jewish scholars are adamant that Mary was not a virgin that gave birth.
In the New Testament, Matthew 1:22-23 (quoting the Septuagint) applies Isaiah 7:14 to Mary, saying she was a virgin. Then Matthew 1:25 confirms that she remained a virgin until the birth of Jesus. Luke provides a different line of evidence for the same doctrine. In Luke 1:34, when Mary was informed by the angel that she would have a child, she asked, "How can this be, since I do not know a man?" In other words, she was a virgin. The angel then went on to explain to her that the Holy Spirit, acting without the agency of any man, would cause the conception to take place, so that her child would be "the Son of God" (Luke 1:35).
Thus, we do not depend on Isaiah alone for the doctrine of the virgin birth.
On the other hand, we have no problem admitting that the New Testament authors relied upon the Septuagint's renderings, at least as much as they depended upon the Hebrew Bible. The point you are wishing to make, if I am not mistaken, is that the Septuagint contained the Apocrypha, and that we should assume that the New Testament writers, who quoted from the Septuagint, must also have accepted the inspiration of the Apocrypha (and thus, so should we).
However, this argument is greatly weakened by the fact that the Septuagint contains books besides your Apocrypha, which are not included in either the Catholic Bible or the Protestant Bible (they are all included only in the Eastern Orthodox Bible). If your argument has weight, then we should accept all the books in the Septuagint. Neither your Bible nor ours include them all. The Septuagint was not necessarily just the Greek Bible. It was a library of Greek Jewish writings of various values, including the canonical books of the Hebrew Bible, the Tanakh (corresponding to the 39 books of the Protestant Old Testament). That the early Christians sometimes quoted the Septuagint's rendering of a biblical text does not mean that they accepted every book in the Septuagint as scripture. Nor should we.