The rejection of established religion in "The Open Boat" is shown by _____, _____, and the descriptions of humans as holy.

We see the rejection of established religion through the repetition of the men's appeal to the "seven mad gods," who they evidently used to believe would operate on some principle of justice, juxtaposed with the injustice of the men's situation. They repeat,

If I am going to be drowned—if I am going to be drowned—if I am going to be drowned, why, in the name of the seven mad gods, who rule the sea, was I allowed to come thus far and contemplate sand and trees?

There is something so unjust about being allowed to survive one's ship sinking only to drown in a lifeboat after suffering so much already. It's ironic and unfair, and the men seem to realize—especially after Billie's death—that their situation is evidence that no such gods exist, that no one cares about whether they live or die except themselves.
We also see the rejection of established religion through the men's reliance on their "subtle brotherhood" rather than a god. No one speaks of it, "But it dwelt in the boat, and each man felt it warm him." They rely on one another in every way, comfortable with the roles the little society they establish within the confines of the boat, and they are comforted only by one another. They are, in fact, they only comfort to be had in the face of harsh natural elements such as the appearance of the shark.

"The Open Boat" regards the arbitrary power of nature as the driving force of life and death rather than subscribing to the notion of an all-powerful "God" belonging to an established religion (like Christianity). In the midst of a stormy night aboard the boat, the text remarks on a man's attitude towards life and death while he is in mortal danger:

When it occurs to a man that nature does not regard him as important, and that she feels she would not maim the universe by disposing of him, he at first wishes to throw bricks at the temple, and he hates deeply the fact that there are no bricks and no temples.

Here, the author makes it quite plain that the text and the characters within believe that nature, not some God casting moral judgments, is the deciding factor in who lives and who dies. This revelation is what deepens one's resentment of the hypocrisy, even the absurdity, of established religious doctrine; this is what makes one want to "throw bricks at the temple."
In addition to the pervasive attitude towards nature as the true "God" of life, the story also conflates the absurd and the sacred to show that religion incorrectly defines both. This question references how the story describes people as "holy," which is true at many points; religious diction is used to valorize camaraderie among the crew. Yet there is also an important relationship between a notion of the "sacred" (holy) and the "profane" (obscene or absurd). At the end of the story, a completely naked man, typically a profane or absurd image, comes to the rescue of the crew. The naked man appears to "shine like a saint" though he is "naked as a tree in winter."
To summarize, Crane and his characters reject established religion by revering nature (rather than God) as the true all-powerful life-force and by conflating absurd and sacred images so that they are one in the same.