Of course it wouldn't occur to you that God inspired the NT writers the same as He inspired the OT writers I suppose, and that He gave them insight into the true meaning of the OT texts and that you are misreading them. You CAN find discussions, even online, of Christian hermeneutics, mostly in Covenant Theology, that go into some detail about the NT readings of the OT and how, actually, in spite of the blind Pharisees and today's Jews, the OT prophets saw things the way the NT writers do. Perhaps I can locate some for you.
Just for a minor point, the disputed "almah" was ALWAYS understood to mean a virgin, until Christ came and the Pharisaical Jews rejected Him and therefore decided to insist it didn't mean virgin but "young woman," ABE: which actually makes no sense, because a married young woman would not be referred to as "almah" and an unmarried pregnant young woman would not be mentioned in such a context at all unless she was a virgin, the miraculous sign the passage calls for.
As I say, the context itself requires that "virgin" be meant.
...the Septuagint (LXX) translates the word "almah" as "young woman".
Well, no it doesn't. The Septuagint's "parthenos" DOES imply virginity.
You'll probably dispute Wikipedia as a source but this is what it has for Isaiah 7:14
The author of the Gospel of Matthew used the pre-Christian Jewish Septuagint's translation of the Hebrew word almah as the Greek parthenos (a word that usually implies virginity)
I doubt the Septuagint had any special influence. The Jews of the day would have known that Isaiah 7:14 referred to a virgin, plus the report of the angel's annunciation has to be treated as a lie to deny it. Which of course the unbelieving Jews did, calling Mary a whore and all that. Kind of leaves you with a choice whether to believe them or the honest disciples of Christ.
Didn't we have this discussion a while back where I produced some evidence of pre-Christian Jewish understanding of the word as "virgin" and you merely dismissed it as irrelevant what a few Jews thought? Guess I should find that first.
ABE: The discussion we had was about the Two Messiahs, not almah.
Within the original context, yes, ABE: but the word is ambiguous no doubt because it has two references, an immediate and a future /ABE. The question is whether the pre-Christian Jews regarded the passage as also messianic, which would explain, for instance, why the Septuagint's Jewish translators used the Greek word normally understood to refer to a virgin. But I'm on a search for other evidence.
If the girl in Ahaz' time was married, "Betulah" which specifically refers to a virgin wouldn't have worked, but "Almah" works for both situations, the current and the future prophetic. The name "Immanuel" is a pointer to its prophetic meaning.
The Old Testament is full of such double references, the prophetic meanings of which the God-inspired New Testament writers brought out. ABE: This can only be properly understood through the Holy Spirit of course /ABE
I'm afraid I was probably thinking of the discussion back in June with Elijahu about the "suffering servant" of Isaiah 53 which WAS understood to be messianic prophecy by pre-Christian Jews, rather than "almah" which isn't discussed in that same book.
There is another book I was looking for that I can't find that may refer to it and if I find it and it does discuss this passage I will post on it, a book by a Christian Jew about pre-Christian rabbinical writings.
Most of the discussions I found online emphasize that for the Jews to translate "almah" as "parthenos" in the Septuagint is a clear sign that they understood the word in that context to mean "virgin," despite all the Pharisaical insistence to the contrary.
Look, when referring to an unmarried young woman, "almah" DOES mean "virgin" but it is ambiguous, depending on context, unlike "betulah," which always refers to a virgin, and I did lose track of the fact that in the context of Ahaz' time the young woman would not have been a virgin because a miraculous conception was not the promise in that context, so she must have been married, and "almah" works for that too. The miraculous context is the future prophetic context and "Immanuel" in that context refers to its meaning, "God with us," which is a description of Messiah. And again, the choice of "parthenos" does show that the Jews understood "almah" to refer to a virgin prophetically. "Parthenos" is also ambiguous, again necessary in the context of God's sign to Ahaz, but also having the connotation of "virgin."
But apparently you don't want to be enlightened about how prophecy works in the Bible, you prefer your one-dimensional view of it.