Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
Well this side of Paradise!...
There's little comfort in the wise
—Rupert Brooke
Experience is the name so many people give to their mistakes.
—Oscar Wilde
As we explained in the "What's Up With the Title?" analysis, the first of these epigraphs comes from a poem called "Tiare Tahiti" by Rupert Brooke. The line refers both to the pleasant idea of a Christian heaven… and the fact that Brooke finds little comfort in this idea, because life on earth just sucks sometimes.
Amory Blaine (the protagonist of this novel) also finds little comfort in the idea of spiritual salvation. He finds it impossible not to dwell on the evils of the world, and he becomes a cynic over time. De-pressing.
The second epigraph comes from Oscar Wilde, and it suggests that life in many cases is just a long series of mistakes that we keep on making. Some people learn from these mistakes and some don't… which means that life experience can either be good or worthless depending on how much we learn from our goofs.
Unfortunately, Amory Blaine has no clue what he's supposed to learn from his life and his mistakes. He lacks all sense of direction, and in many cases, he doesn't even know whether or not he's made a mistake. Double epigraph, double dose of depressing.