I am not a practising Christian
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At least, not in the pianistimo mode! Still, that did make for stimulating conversation.
In the context of what you wrote, what do you do then with Matthew's remark about Isiah's verse being indeed a prophecy?
Several things. First of all, he says it's from the prophet. You have to understand something that may not be obvious. Prophecy is not prediction. Prophecy is merely greater access to the will of God than most people, it has nothing to do with the future.
Secondly, Matthew despite obviously being fluent only in Greek is writing in the Hebrew midrash tradition, which requires that stories always be set in the context of earlier ones to emphasize their importance and the continuity of the people. This is common in Old Testament writings, but often missed in NT. The scriptures must be read within the context of the times, the culture, and the language. Of course, a significant subset of American Christians eschew scholarship and violently disagree, feeling ANYONE can read with equal understanding, because the Holy Spirit will guide us. Apparently he guides us all in different directions.
Thirdly, Isiah did not say virgin. He used the term young woman, which does not connote virginity. Matthew who was working with a Greek version simply misinterpreted. Well, since Matthew and Luke copied much of Mark, who copied Q, wellllllllllllllllll never mind.
Isn't that the reason nobody among the believers is asking questions?
I'm sure you realize asking questions is frowned upon among believers.