Explain Paul’s inner-struggles while in the shell-hole?

Paul's initial descent into the hole brings him a sense of remorse and shame, which is ultimately overcome by the safety of his location. When he hears the voices of his comrades, he feels enormous loneliness in his isolation. After stabbing the other soldier and finding he's still alive but quickly dying, Paul find his generosity of nature and his ability to empathize. He tries to bring the other man comfort, to ease his death. It is at this point that Paul truly understands what it means to take the life of another, to be responsible for another's death.