why do you think at this point ahab makes this revelation of himself? What might have prompted this confession of self?

In a sense, Ahab seems to give his last words to Starbuck. Even before the battle with the white whale, Ahab has written his own requiem, presaging his own death at the hands of Moby Dick and hoping for a better afterlife. Ahab's imagery of heaven, in particular his allusion to sleeping on the fields, recall mythic imagery of the Elysian fields. Once again providing a parallel to mythic heroes, Ahab fancies himself not in Christian ideas of paradise but in the afterlife of classical mythology.