Moby-Dick isn't the Great American Novel—it's The Great Novel. It's themes are too universal, too utterly human to be confined to those of a single nation. It's not even clear Melville was just writing a novel: his masterwork is a hymn, a poem, a philosophical treatise, a celebration of the sea, and a mystical adventure of the soul as terrifying and powerful and unknowable as the White Whale himself.
From the opening line ("Call me Ishmael.") to the haunting last chapter, we're gradually drawn away from everything we know about ourselves and the world, and into a beautiful wilderness of words, images and ideas both ancient and modern. The hunt for Moby-Dick perpetrated by Capt. Ahab and his crew is not just a common whaling voyage or even just an uncommon revenge tale. What Ahab wants to subdue is not an enigmatic whale—it's the secret and meaning of life, death, evil and God. But he's lost at sea with the rest of humanity.
Melville was an innovator, manipulating language the way Ahab manipulates his men, making it do whatever he wanted. Ishmael ostensibly narrates, but at times his voice seems to fade into another and whether it's Melville's or some other we're hearing is anyone's guess. Information Ishmael couldn't have is described in detail, including events which transpire in Ahab's cabin, a sort of demonic holy of holies from which he emanates to direct the Pequod like a pagan god visiting terrified congregants.
Some critics complain there's too much detail. This is only true if you're looking for a conventional story. What Melville offers instead is an evocation, an exploration, a quasi-religious experience. That's not to say the book is formless—it's not. In fact, there's more excitement here than in a lot of what pass for adventure stories: scenes of whale hunts, attempted mutiny, storms, the mystery of St. Elmo's fire, Ahab's charismatic speeches. But none of these elements (or the descriptions of whaling tools, species of whales, etc.) exist in the narrative for their own sake; each is symbolic of something else, something more fundamental and more universal than the representation.
The White Whale himself, of course, is the central symbolic figure, though his identity remains as mysterious to readers and critics as Melville's limited and baffled readership found him initially. The trouble is wanting him to be something specific, to have one purpose in the story, when in fact Moby-Dick represents many things, some of them contradictory. He represents Ahab's madness, the crew's blind obedience, the destructive force of the ocean. But his identity goes much deeper: Moby-Dick is human sin, man's obsession with evil, the soul of innocence, and of guilt, and death. Moby-Dick is human nature embodied, and Ahab's relentless pursuit is the struggle for self-identity, the knowledge of good and evil, the knowledge of God.
Uncovering the many facets of the Whale's symbolism in a paragraph is as pointless and impossible as Ahab's insane quest. This isn't a typical novel with "good guys" and "bad guys" and a central conflict. This is Melville's attempt at cosmology, a philosophical investigation that is also an aesthetic masterpiece, and understanding it is as spiritual and intuitive as Ishmael's bond with Queequeg. When people reference "great literature," this is the kind they're talking about. A book to take your breath away, Moby-Dick is one of the great works of human imagination.