I'm going to comment on Richard Carrier's discussion of the virgin birth prophecy:
i) It's striking that an unbeliever would imagine that Carrier a good person to ask about Isaiah 7:14. To begin with, since Carrier is an atheist, his naturalistic interpretation is a foregone conclusion.
ii) In addition, Carrier is a Classicist, not a Hebraist or OT scholar. He has no expertise on Isa 7:14.
iii) One problem with a naturalistic interpretation of Isa 7:14 is that, even though an atheist denies inspired foresight, Bible writers, and ancient Near Easterners generally, did believe the future could be foreknown by supernatural means. When secular interpreters come to a passage like this, they confuse what they think is possible with what Isaiah believed. But when you interpret Isaiah, even if you don't believe Isaiah, you need to interpret his oracles as he understood them, consistent with his worldview. Even if you don't think his oracle could be genuinely prophetic, you must respect what he intended. That's what exegesis is all about. Ascertaining what the original author had in mind.
I'll bet we have dozens if not hundreds of occasions where almah is used, in and out of the OT, where we can't know if the denoted girl was a virgin or not.
In other words, he hasn't actually studied the frequency of OT occurrences. This is just his seat-of-the-pants hunch.
Moreover, the fact that the Hebrews saw a need to coin a word more definitely meaning 'virgin' (bethulah) implies that almah did not definitely mean virgin.
i) Carrier offers no evidence for that claim. Even a liberal scholar like Brevard Childs, in his commentary on Isaiah, says "it is very unlikely that a married woman would still be referred to as an almah…the preferred modern translation of 'young woman' (NRSV) is too broad a rendering since it wrongly includes young wives" (66).
ii) Moreover, the exact rendering of almah is something of a red herring, for that fails to draw a rudimentary distinction between sense and reference. Even if almah doesn't mean "virgin," a virgin can be the referent.
For instance, Secretariat doesn't mean "horse," yet Secretariat refers to a horse. A horse is the designatum or denotatum of Secretariat. By the same token, a virgin can be the denotatum of almah even if that's not what the word means.
iii) In addition, we need to distinguish between denotation and connotation. Even if almah isn't a synonym for "virgin," it can have presumptive virginal connotations in a culture where premarital sex was punishable.
iv) Moreover, Carrier fails to take the larger context into account. The oracle is introduced as a "sign" or prodigy (v11). Compare that to the healing of Hezekiah–a promise attested by the prodigy of the sundial (Isa 38). A miraculous sign to portend a miraculous healing. That's the thought-world in which Isa 7 is moving.
v) Furthermore, it doesn't end with Isa 7. The career of this mysterious child continues to be charted in chaps 8-9, & 11. This is no ordinary child. His career extends generations beyond the exigent circumstances of Isa 7.
…since Isaiah can be interpreted non-supernaturally even if he did mean virgin. After all, is it really unusual for a virgin to conceive? Say, on her wedding night? True, then she isn't a virgin anymore. But she was until she conceived (literally, not at that very moment, but the Bible is rarely so precise). Since conception does not always occur the first time it would still be significant to say that a virgin conceived, meaning only that she conceived the first time she was with a man.
In reference to the virgin birth of Christ, which is Carrier's real target, that's confused:
i) In principle, there's an asymmetrical relation between the virginity of the mother and the virginal conception of the child:
The virginity of the mother entails the virginal conception of the child;
However, the virginal conception of the child does not entail the virginity of the mother.
Even if the mother was not a virgin at the time, you could still have a virginal conception so long as that took place apart from sexual reproduction.
A virginal conception doesn't require a virginal mother. It only requires that in that particular instance, the conception was not the natural result of a man impregnating a woman. In principle, you could have a virginal conception even if Mary was not a virgin. These are not mutual entailments.
ii) The primary function of Mary's virginity is to safeguard the fact that Jesus was conceived without a father. Although that's metaphysically possible even if Mary had had previous children by sexual reproduction, her virginity ensures that Christ's conception was virginal. Even though her virginity isn't a necessary precondition for the virgin birth, it renders certain the fact that Christ had a mother, but no (human) father.
In the providence of God, these separable elements (virgin mother, virginal conception) were combined to remove any ambiguity regarding the virginal conception of Christ.
iii) In context, the virginity of Mary refers, not simply to the fact that she hadn't had sexual relations before then, but that she didn't conceive by means of sexual relations.