In A Farewell to Arms, the priest in some ways is like a foil to Lt. Frederic Henry. The priest tells Lt. Henry that he believes in God and that much of what he does revolves around his belief. Lt. Henry, on the other hand, does not really know what his life's purpose is, and as a result, Lt. Henry struggles with defining his own identity. When they meet, the priest tries to help Lt. Henry find himself, but Lt. Henry is too skeptical about the war and about life to accept any easy answers. That said, Lt. Henry is moved by the priest's ability to believe in something, and eventually, Lt. Henry is able to believe in the love that he has for Catherine Barkley.
The priest in A Farewell to Arms, a character with no specific name other than "the priest," is the voice of conscience. While the soldiers make fun of him, he is stoic and even good-natured as he blushes about their jokes poking fun at his celibate life. When the priest comes to visit Frederic Henry (when Henry is wounded and lying in pain in the field hospital in Chapter 11), the priest brings Henry vermouth, English newspapers, and mosquito netting. In the conversation that follows, the priest tells Henry that he hates the war and that there are two kinds of people: "There are people who would make war. In this country there are many like that. There are other people who would not make war" (page numbers vary by edition). The priest pushes Henry to reconsider his own views about the war and about the nature of love. When Henry describes the way he feels about love, the priest tells him that he doesn't yet understand that true love involves sacrifice.
The priest's conversations with Henry change the way Henry thinks about the war and about love, and they also show that the priest is a deep-thinking person who understands the futility of war and the essential quality of love. The priest is young, but wise and full of love, as he only hopes that Henry and the other soldiers emerge from the war unharmed, despite the soldiers' relentless mockery of him.