[
UPDATE: Note that the statement below that the Dead Sea Scrolls has the word "virgin" appears to be incorrect. I am leaving my comment as is, but please note that when reading it. The other points made here still hold.]
The Septuagint is the translation used by the Orthodox church. Also referred to as the "Greek Old Testament", it is a translation made by Jews in the 3rd century B.C. from the original Hebrew OT into Koine Greek. Again, the translation dates back to
the 3rd century B.C.
The Masoretic text, or the Hebrew Old Testament, is the version used both by Jews but also by most Protestants. The earliest Masoretic text manuscripts date only to the
9th century A.D. (that's
A.D., not
B.C.). So the Septuagint preserves a
much earlier version of the Hebrew in Greek translation. The Masoretic text continued to be revised and edited throughout history, so the versions we see may vary considerably from the original versions.
And, highly relevant in this context, Jewish rabbis continued to revise the Masoretic text in response to Christianity: i.e. they made changes in order to refute and undermine the claims of Christians. One of these changes was taking out the word "virgin" and using "young woman."
The Dead Sea Scrolls (from around 1-2 c. BC to 1st c AD), which are much earlier manuscripts than the transmitted Masoretic text, confirmed this to be the case. From Wikipedia: "there was indeed a Hebrew text-type on which the Septuagint-translation was based and
which differed substantially from the received MT. The scrolls show numerous small variations in orthography, both as against the later Masoretic Text, and between each other.
It is also evident from the notings of corrections and of variant alternatives that scribes felt free to choose according to their personal taste and discretion between different readings."
Specifically, the Dead Sea Scrolls confirmed that the word "virgin" had originally been in the text, and was subsequently changed in the MT. From an editor's footnote to Blessed Theophylact's commentary on the Gospel According to St. Matthew: "
Note: the Hebrew text of Isaiah found among the Dead Sea Scrolls at Qumran in 1947 does confirm the accuracy of the Septuagint reading of "virgin"."
And speaking of Blessed Theophylact, his commentary also confirms that this same debate has been going on for 1,000 years: Theophylact's commentary (which is really really good), dates to the 10th century.
Blessed Theophylact makes the point that whether the word used is "virgin" or "young woman", the prophecy only makes sense when interpreted to mean "virgin". Why? Because there is nothing incredible or unusual about a "young woman" giving birth to a child. What made Isaiah's prophecy so marvelous and indicated that it was a "wonder" and a "sign" is precisely that she was a virgin.
Here is the full text of Blessed Theophylact's commentary on the relevant passage from Matthew 1:23:
"The Jews say that it is not written in the prophecy "virgin" but "young woman". To which it may be answered that "young woman" and "virgin" mean the same thing in Scripture, for in Scripture "young woman" refers to one who is still a virgin. Furthermore, if it was not a virgin that gave birth, how would it be a sign, something extraordinary? Listen to Isaiah who says, ''For this reason the Lord Himself shall give you a sign,'' and immediately he adds, ''Behold, the Virgin.''18 So if it were not a virgin that would give birth, it would not be a sign. The Jews, then, alter the text of Scripture in their malice, putting "young woman" instead of "virgin".19 But whether the text reads "young woman" or "virgin", it should be understood in either case that it is a virgin who will give birth so that the event may be a miraculous sign."
Footnote 18 is the citation to Isaiah 7:14. Footnote 19 is the wording I provided above about the Dead Sea Scrolls confirming the antiquity of the original word "virgin" in Isaiah.