Moby dick is an encyclopedia of everything, history, philosophy, religion, etc. but it is first a Shakespearean tragedy of man fighting against overwhelming odds in an indifferent and even hostile universe.
1.Moby dick is a sprawling colossus into which the author kept dumping everything he saw as necessary to prove his point.
2. Moby dick represents the sum total of Melville’s bleak view of the world in which he lived. It is at once Godless and purposeless. Man in this universe lives a meaningless and futile life, meaningless because futile.
3. One of the major themes in Melvilles is alienation, which he sensed existing in the life of his time on different levels, between man and man, man and society, and man and nature.
4.Moby Dick reveals the basic pattern of nineteenth-century American life: loneliness and suicidal individualism in a self-styled democracy.

Written by one of America's greatest authors, Moby-Dick is a work of tremendous power and depth-one of world literature's great poetic epics. In the novel, published in 1851 after sixteen months of writing, Herman Melville recounts the Promethean quest of Captain Ahab, who, having lost a leg in a earlier battle with White Whale, is determined to catch the beast and destroy it. By the time readers meet Ahab, he is a vengeful, crazed, and terror-provoking figure, for Moby Dick has come to represent for him all the evil in the world.
The relentless voyage of Ahab and his crew, a finely etched group of weird and wonderful characters who seem both flesh-and-blood individuals and symbolic of the varying qualities of men, becomes a masterful drama of life at sea. The drama is made more fascinating by Melville's eloquent style-a combination of the journalistic, colloquial, and poetic-and the themes and subjects he pursues-whales and whaling; mean's need for love and comradeship; and the fury of Ahab for the whale.
Through realistic storytelling, symbolic allegory, and allusive and figurative language, Melville achieves in Moby-dicka special intensity that readers will marvel at, and not soon forget.

Moby-Dick is a highly symbolic work, and is interesting in that it also addresses issues such as natural history. Other themes include obsession, religion, idealism versus pragmatism, revenge, racism, hierarchical relationships, and politics.
Symbolism
All of the members of the Pequod's crew have biblical-sounding, improbable, or descriptive names, and the narrator deliberately avoids specifying the exact time of the events and some other similar details. These together suggest that the narrator—and not just Melville—is deliberately casting his tale in an epic and allegorical mode.
The white whale itself, for example, has been read as symbolically representative of good and evil, as has Ahab. The white whale has also been seen as a metaphor for the elements of life that are out of our control, or God.[citation needed]
The Pequod's quest to hunt down Moby-Dick itself is also widely viewed as allegorical. To Ahab, killing the whale becomes the ultimate goal in his life, and this observation can also be expanded allegorically so that the whale represents everyone's goals. Furthermore, his vengeance against the whale is analogous to man's struggle against fate. The only escape from Ahab's vision is seen through the Pequod's occasional encounters with other ships, called gams. Readers could consider what exactly Ahab will do if he, in fact, succeeds in his quest: having accomplished his ultimate goal, what else is there left for him to do? Similarly, Melville may be implying that people in general need something to reach for in life, or that such a goal can destroy one if allowed to overtake all other concerns. Some such things are hinted at early on in the book, when the main character, Ishmael, is sharing a cold bed with his newfound friend, Queequeg:
... truely to enjoy bodily warmth, some small part of you must be cold, for there is no quality in this world that is not what it is merely by contrast. Nothing exists in itself. If you flatter yourself that you are all over comfortable, and have been so a long time, then you cannot be said to be comfortable any more.
— Moby-Dick, Ch. 11
Ahab's pipe is widely looked upon as the riddance of happiness in Ahab's life. By throwing the pipe overboard, Ahab signifies that he no longer can enjoy simple pleasures in life; instead, he dedicates his entire life to the pursuit of his obsession, the killing of the white whale, Moby-Dick.
A number of biblical themes occur. The book contains multiple implicit and explicit allusions to the story of Jonah, in addition to the use of certain biblical names (see below).
Ishmael's musings also allude to themes common among the American Transcendentalists and parallel certain themes in European Romanticism and the philosophy of Hegel. In the poetry of Whitman and the prose writings of Emerson and Thoreau, a ship at sea is sometimes a metaphor for the soul.