So, re-reading these chapters was shocking to me. If what I write about them shocks you, it means you're paying attention.
1. 2 Nephi 17. Ahaz's situation is like that of the Judahites at the end of the monarchy (Zedekiah, etc.), trapped between foreign powers. Ahaz is told to ask a sign of the Lord (DSS Isaiah: a sign of the Lord's mother, remember?). The sign is the Virgin ("the" Virgin, in Hebrew and Greek, not "a" virgin) who shall bear a child, like 1 Nephi 11. Desolation will come on Ahaz and his people.
2. Incidentally, "virgin" in Hebrew is "'almah". This is interesting, because it occurs to me that THREE of the Book of Mormon names might be references to the Virgin. 1) Alma. 2) Nephi, because nfr in Egyptian is fair, nfr was pronounced "something like nafi" by Lehi's time, and the Virgin in 1 Nephi 11:13 is described as "fair". 3) Best of all, Laban is a Hebrew word meaning "white". So actually, "Laban" and "Nephi" are the same name, in Hebrew and Egyptian, "the white one". This is not really surprising, since they're family, and it makes me wonder if Nephi's family had a particular devotion to the Virgin.
(And of course, the entire people of the "Nephites" have a name that calls out devotion to or memory of the Virgin.)
3. 2 Nephi 18. Let me parse this carefully.
A) Note the classic sexual symbols in 18:1. The "man's pen" should be obvious, but a "great roll" is a spiral, a classic symbol of the female generative matrix. This chapter is going to be earthy.
B) This chapter follows right on the prophecy of "the Virgin" bearing a son and is about "the prophetess" bearing a son. I do not think this is an accident. I think this is the second half of the same story.
C) I do not think "the prophetess" was Mrs. Isaiah. The OT refers to various prophetesses (Miriam in Exodus 15:20, Deborah in Judges 4:4, Huldah in 2 Kings 22:14 (and Chronicles), etc.), and none of them is Mrs. Prophet -- they are prophetesses in their own rights. The woman in Isaiah 8 is definitely THE prophetess, in both Greek and Hebrew, in the same way Isaiah 7 talks about THE virgin. It's difficult, reading them back to back, to think they aren't connected. Since 17:14 says "the Virgin shall conceive" and 18:3 says "I went into the Prophetess and she conceived", it's very difficult for me think they aren't, in fact, the same person. Or rather, it seems to me that the Prophetess must have been a figure in Jerusalem something like the High Priest, and just as the High Priest was / represented Yahweh on the Day of Atonement, the Prophetess was / represented the Virgin on certain occasions.
D) The occasion in particular is not an ordinary conjugal encounter. In addition to the fact that it's the object of prophesy and tied to the giving of signs to a king making crucial foreign policy decisions (you think YOU feel pressure, lads? ha!), there are WITNESSES (18:2). This is a formal act, and I think a ritual one. It looks like a hieros gamos, straight out of Anthropology 101 (hieros gamos is fancy Greek for "sacred marriage"), in other words, human priests and priestesses acting out a heavenly marriage (complete, yes, with child-conceiving acts) on behalf of or standing in for the gods. (The Da Vinci Code had an amusing, but not totally false, hieros gamos as one of its plot components.)
E) What would be the point of such a hieros gamos in Jerusalem? I believe that ancient Israel knew a trinity of father-mother-son, which shows pretty clearly in 1 Nephi 11. I think the point of a hieros gamos for ancient Israel would be the sign and miracle of the Virgin, in the person of her servant the Prophetess, conceiving and bearing a child. Who is this child? Nephi tells us, in 1 Nephi 11... the baby, the fruit of the tree, is the Lord Yahweh, the son in the ancient Israelite trinity.
F) Isaiah and the prophetess conceive a son who isn't actually the Lord, but is given a prophetic name to indicate that, despite Yahweh's still-delayed appearance, he's coming soon, with judgment, on the Day of the Lord (reminds me of 2 Nephi 6:13, which defines Yahweh's people as those who wait for him).
G) The prophet, prophetess and the child are "signs and wonders" (18:18). Remember 1 Nephi 19:13, that caught my eye the other day. Maybe what the Judahite leaders in Jerusalem rejected specifically was this "sign and wonder", the Virgin and her child, the Lord.
(H) And of course, the Second Temple Israelites who would become the first Christians remembered the prophecy of the Virgin and her son, and applied it (correctly, per Nephi) to Mary and Jesus. Only later Christians, having lost the plot, concluded that Mary magically and physically remained a virgin her entire life, despite having various children.)
I'm thankful for a lot of things today. Let me mention four, quickly: my wife, Emily; my family; my country; and the Book of Mormon, which cuts right through the snarl of the re-writing and deception and age that tangles up the Bible and shines a spotlight on the ancient history of Israel.
Happy Thanksgiving, all.