At this point I think I understand Melville's attitude towards Paganism and also his theological symbolism. Offeror's posts have made me think about Melville's theory of fate. The problem, as we have discussed, is that there is a recognizable Shakespearean tragedy going on, with its combination of choice and fate; but there also many purely fatalistic overtones to the narrative. These episodes are sometimes expressed in terms of Biblical Prophecy (Elijah vs. Ahab, etc.). I suggested (baffled as usual) that it almost seems like Melville was giving his reader a choice.
I refined that opinion recently when I remembered the scene from Chapter 47 in which Ishmael and Queequeg are weaving together (a la the Fates). There is no reason to debate symbolism because Ishmael explains it all:
"As I kept passing and repassing the filling or woof of marline between the long yarns of the warp, using my own hand for the shuttle, and as Queequeg, standing sideways, ever and anon slid his heavy oaken sword between the threads, and idly looking off upon the water, carelessly and unthinkingly drove home every yarn; I say so strange a dreaminess did there then reign all over the ship and all over the sea, only broken by the intermitting dull sound of the sword, that it seemed as if this were the Loom of Time, and I myself were a shuttle mechanically weaving and weaving away at the Fates. There lay the fixed threads of the warp subject to but one single, ever returning, unchanging vibration, and that vibration merely enough to admit of the crosswise interblending of other threads with its own. This warp seemed necessity; and here, thought I, with my own hand I ply my own shuttle and weave my own destiny into these unalterable threads. Meantime, Queequeg’s impulsive, indifferent sword, sometimes hitting the woof slantingly, or crookedly, or strongly, or weakly, as the case might be; and by this difference in the concluding blow producing a corresponding contrast in the final aspect of the completed fabric; this savage’s sword, thought I, which thus finally shapes and fashions both warp and woof; this easy, indifferent sword must be chance— aye, chance, free will, and necessity—no wise incompatible— all interweavingly working together. The straight warp of necessity, not to be swerved from its ultimate course— its every alternating vibration, indeed, only tending to that; free will still free to ply her shuttle between given threads; and chance, though restrained in its play within the right lines of necessity, and sideways in its motions directed by free will, though thus prescribed to by both, chance by turns rules either, and has the last featuring blow at events."
So there on the surface of it is Melville's theory of fate or, more accurately, Augustine's. Melville is willing to accept "chance, free will, and necessity—no wise incompatible— all interweavingly working together." This combination allows Ahab's tragedy to unfold within the western literary model.
But then the darnedest thing happens. As they are weaving away on deck, Tashtego, the Gay Head Indian, sings out the Pequod's first sighting of whales. Ishmael says: "you would have thought him some prophet or seer beholding the shadows of Fate," and notes "the ball of free will dropped from my hand, and I stood gazing up at the clouds whence that voice dropped like a wing."
So perhaps the reader does not get a choice between theories of fate. Perhaps Melville is expressing a distinction in terms of mode. There is the "limited will mode" (chance, free will, and necessity) which permits Ahab in his cabin or back in Nantucket to weave his own destiny, and then there is--the combat model?; the Biblical model?; the whaling model? What happens, in any case, when one is so removed from the possibility of meaningful choice that the ball of free will drops right out of the boat and there is only necessity and chance.
This modular approach to fate would (finally) explain why Ishmael survived the Pequod's destruction. He was fated to survive; others were not. So perhaps I have made progress with that mystery as well. And perhaps it is compatible with your idea that there was no special reason that he survived--unless fate--blind or otherwise--can be thought of as a special reason.