The pursuit of the great white whale, in whom Ahab imbues preternatual powers, is a metaphor for the conflict between man and the power of nature, between man and his own fate. For Ahab, orphaned at a young age and having lived on ships most of his life, the sea represents the universe. In Chapter 36, "The Quarter Deck," of Moby Dick, Ahab tells his crew,
"All visible objects, man, are but as pasteboard masks. But in each event--in the living act, the undoubted deed--there, some unknown but still reasoning thing puts forth the moldings of its feature from behind the unreasoning mask. If man will strike, strike through the mask! How can the prisoner reach outside except by thrusting through the wall? To me, the White Whale is that wall, shoved near to me. Sometimes I think there's naught beyond. But 'tis enough. He tasks me; he heaps me; I see in him outrageous strength, with an inscrutable malice sinewing it. That inscrutable thing is chiefly what I hate."
Ahab would know the mysteries of nature, a nature that is often a dark force against man. By breaking through the "pasteboard mask" of the whale and other natural forces, Ahab hopes to understand existential meanings, to make some sense of existence and man's role in this mysterious world. He pursues Moby Dick, a metaphysical force that knows the depths of the sea, a symbol of existential consciousness, to whatever destiny may bring. Thus, Ahab's quest is biblical and epic in nature.