After Henry runs away from battle and is in the midst of rationalizing his behavior, he comes across a particularly tranquil spot in the woods:
At length he reached a place where the high, arching boughs made a chapel. He softly pushed the green doors aside and entered. Pine needles were a gentle brown carpet. There was a religious half light (7.18).
Aw. Peaceful, holy, serene… and then… "A dead man [with] eyes […] changed to the dull hue to be seen on the side of a dead fish" (7.20). Oh, and there are ants crawling into its eye sockets and mouth (reminiscent of Indiana Jones and the Temple of Doom).
This is where Henry comes to realize that nature and the universe have no interest in this dead man, nor do they have an interest in whether Henry himself lives or dies. There is simply nothing out there to help or save him or anyone else. This is a shocking lesson for him, and one that shatters his notions of the way things work.
This is also Crane’s way of introducing the philosophy of "Naturalism" into the novel -- Naturalism says that literature should present human beings objectively, in fact, even scientifically. Naturalists were largely influenced by Darwin’s theory of evolution, which places a strong emphasis on biological determinism. Literary Naturalists reject the notion of free will and see humans as controlled primarily by instinct, emotion, and (occasionally) cultural conditions. This idea makes Henry’s behavior more a matter of random and explainable phenomena, rather than a growth toward maturity, or a rise toward heroism, via free choice/decision.
As Henry encounters even more death, he finds that the cessation of life is only an integral part of human existence: "He had been to touch the great death, and found that, after all, it was but the great death" (24.31). He realizes that regardless of bravery or courage, the world has one plan for all things and that plan always ends in death. Crane loves to imply this idea via images of nature’s beauty contrasted with man’s bloody brutality, and he capitalizes on this paradox many times throughout the novel.
Since Crane was a big believer in Naturalism, he wanted to show that death should not be romanticized, but should be looked at straight on in as dispassionate and scientific a way as possible. The postures and paroxysms and vulnerabilities of dead men make death seem like a very real physical phenomenon, rather than a spiritual departure involving heaven or hell. Henry, too, is affected by viewing the dead. He sees that the dead know no more than he does, and that nothing supernatural happens to them. He also realizes that he could just as easily be among them -- that dying is as random and meaningless as war, or anything else.