What does Ahab hope to achieve by battling nature's mysteries in Moby Dick?

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.