In Moby Dick, there is a heavy emphasis placed on the concept of depth. The word depth itself appears (as depth or depths) about 20 times through the novel; considering the nautical nature of the story, one would honestly probably expect it to turn up far more frequently. This is a good clue that Melville has used it sparingly to be cautious with how it is used, rather than simply coincidentally. Melville attempts to use the word “depth” to connect readers' interpretation of the physical story with an interpretation of their idea of God.
The first occurrence of the term is during Father Mapple's sermon on Jonah and the whale. He says “...one of the smallest strands in the mighty cable of the Scriptures. Yet what depths of the soul does Jonah's deep sealine sound!” Father Mapple clearly is intertwining nautical imagery and language with an underlying spiritual meaning. Melville is showing a character who very clearly puts great import on words; Father Mapple believes the depth of the ocean to be a metaphor, perhaps for God's power or for the power of a person who works with God. The most significant aspect to this usage of the word depth is that it depicts a dimension both of the sea and of one's soul. Of course, physical depth representing metaphorical or spiritual intensity is not a new concept. Deep objects, especially the sea, are very frequently compared to people's emotions and thoughts. However, this immediately sets a tone for the rest of the novel; depth is clearly a word to be interpreted as having multiple implications.
The next unique appearance of the word depth appears in Chapter 41, “Moby Dick.” In this chapter, we learn Ishmael's experience with the great white whale. Depth appears in a very intellectual discussion of the whiteness of the whale, “Is it that by its indefiniteness it shadows forth the heartless voids and immensities of the universe, and thus stabs us from behind with the thought of annihilation, when beholding the white depths of the milky way?” This is Ishmael's personal struggle. He is attempting to come to terms with both his own connection to the whale and the terror of the whale's pure whiteness. This is very reminiscent of a religious struggle; individual men must come to terms with their own personal connection to God and the terror that some of God's deeds induces.
Depth rears its head again in Chapter 82, “The Honor and Glory of Whaling.” This time, he appears in a discussion of another God. “...so Vishnoo became incarnate in a whale, and sounding down in him to the uttermost depths, rescued the sacred volumes.” Once again connecting the physical presence of the whale, deep in the ocean, to the spiritual presence of God, deep within man. This solidifies Melville's connection between depth and God in a much more blatant way, addressing the actual name of an extant god.
Again we see depth appearing, in Chapter 87, The Grand Armada. “The lake, as I have hinted, was to a considerable depth exceedingly transparent; and as human infants while suckling will calmly and fixedly gaze away from the breast, as if leading two different lives at the time...” Melville is almost directly addressing the idea of a dual consciousness; a consciousness of both what is occurring in the visible, clear, top portion of the water and what is occurring below the level of consciousness. This is very blatantly to be compared to man's physical consciousness of his existence and his spiritual consciousness of (and faith in) the existence of a higher spiritual power, or God.
Much like Father Mapple, Melville is attempting to achieve an effect on his audience by embodying a previously meaningless word, depth, with heavy-handed meaning. Melville very clearly struggles with his image of God in many of his works. In Moby Dick, he interlocks discussion of physical depth with discussion of God, hoping most likely to describe man's struggle to connect their physical and visceral experience with the highly philosophical God that they answer to.
(I used an e-text for reference while I wrote this entry, so I don't have page numbers. If necessary, I can find my text at a later date and add the page numbers in to cite my quotes properly.)