Moby-Dick is, fundamentally, a revenge tragedy. It’s about one man’s maniacal obsession with vengeance. It’s about finding an object on which to pin all your anger and fear and rage, not only about your own suffering, but also about the suffering of all mankind. It’s about the inability to understand that you can’t punish the natural world, and that Nature isn’t specifically malicious, just impersonally brutal. It’s about the way that the desire for revenge can eat away at you until it becomes something inhabiting your body, something separate from your own personality.
Ahab’s quest for revenge on the White Whale is impossible from the beginning, because it’s foolish to try and wreak vengeance on a non-sentient animal in the natural world.
Ahab’s quest for revenge on the White Whale represents mankind’s struggle against the cruelty and arbitrariness of fate and human suffering.