On a surface level, Moby Dick is about obsession. Referring to Melville's bigass novel, just to be clear. "Jaws" is basically "Moby Dick" with a shark substituting for a whale. Quint was dumped in the Pacific with the sailors of the Indianapolis. Most of his mates became shark food; Quint survived, and waged a vendetta against sharks -- the "Jaws" terrorizing Amity, specifically. Jaws ate him. Moby Dick ate Ahab's leg. Ahab launched a vendetta against the great white whale. With the exception of Ishmael, the crew wound up dead; Ahab wound up harpooned to the whale.
On a deeper level, it's a mad little allegory about the Calvinistic clockwork universe. God is the mad watchmaker; if it's God will that a whale eats your leg, you should deal with it. It's entirely possible there's no watchmaker behind the mad machine. You should deal with that, too. Revenge against God and/or the universe is just plain stupid.
The whale is other. Inhuman. Like the sentient ocean in Solaris, it can't be analyzed. It's also bigger than you are. You lost a leg? Too bad. You will not beat up the universe. You will not beat up God. Don't try.
This is second hand knowledge, English major lore. I've read a seriously condensed edition with Kool illustration. I've seen boththe John Huston movie and the Mister Magoo adaptation. I've even read Ray Bradbury's script for the John Houston movie. Cool script. I've never actually read the original, unedited novel.
Ron Howard. Wow. What a wasted opportunity.