The characters of the chaplain, in Albert Camus The Outsider, and the priest, in Franz Kafkas The Trial, are quite similar, and are pivotal to the development of the novel. These characters serve essentialy to bring the question of God and religion to probe the existentialist aspects of it, in novels completely devoid of religious context. The main idea visible about these two characters is that they are both the last ones seen by the protagonists, Mearsault and K. , both non-believers in the word of the lord.
Whereas the chaplain in The Outsider tries to make Mearsault believe in the existence of god, the priest tries to warn and explain to K. what will happen to him. The reason the chaplain is the last one to see Mearsault is becasue its his job to let the prisioners have a final shot at redemption before they are executed. The reason that K. meets with the priest is out of advice given to him by someone, and he is the last character that he shows K. interacting with (although it might be true that K. eets and interacts with other people after the meeting, but hey are neither mentioned nor visible later on).
The priest doesnt try and make K. confess or anything of the sort, he is mainly there to converse with the character, his religious position is almost put to no use. The existentialist view of religion is that humans have been alienated from god, from each other, and so forth. In the novel Crime and Punishment, by Fyodor Dostoevsky, the christian idea of salvation through suffering is omnipresent throughout the novel.
What is visible with The Trial and The Outsider is that they dont touch on the aspect f religion much throughout the story (The Outsider has bits and pieces of it appearing in his cross examinations but they are used more to mock than in an analitical sense). The presence of these two characters at the end of the novel serves to cover all the existentialist areas known to existemtialists (although it is doubtful whether the authors consciously attempted to make the characters present because of any existentialist rules they had to follow). The characters are required to structure the novels, beside the obvious existentialist areas.
The characters are there to let the protagonists blow off some steam. In all the beaurocracy, confusion, and incompetence these two remain as the only ones that understand the predicament of the protaganists. They actually seem to understand what the protagonists are going through. The priest is more direct, yet symbolic, with K. , telling him a story laden with symbolism and telling him what hes about to go through. The chaplain tries to take advantage of what he understands about Mearsault, and take control of his ideas in his final moments.