This essay does not mention the matter of Isaiah 7:14 and it its use in Matthew 1:23, but it is indirectly relevant. The word used in Isaiah 7:14 means a "young woman" (who may or may not be a virgin). The word betulah is not used. The Septuagint mistranslates that word into Greek as parthenos, which does mean "virgin." Matthew's exegesis depends on the meaning of the Greek word. See here, here and here for more.
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