At last Henry's character changes fundamentally during the course of the summer he spends with Catherine; on the heels of his traumatic experience at the front, a love affair with a woman (rather than mere sex with prostitutes) forces him to grow up for good. This change is demonstrated at the start of Chapter XXXIV, after Henry's desertion from the Italian army. Of the hostile aviators with whom he shares a train compartment, he says that "in the old days I would have insulted them and picked a fight." Now, no longer insecure due to his experiences in love and war, he does not even feel insulted. In fact, as his talk with Count Greffi reveals, the once-indifferent Henry has truly found something to believe in. He tells the Count that what he values most is someone he loves and that he "might become very devout," elaborating that his religious feeling comes at night. Like Catherine, Henry has made a religion of their love. For that matter, he has replaced his loyalty to the Italian army with loyalty to Catherine.
In Switzerland, Catherine suggests she and Henry wear their hair the same length, so as to be more alike. "Oh darling," she says, "I want you so much I want to be you too." Henry replies, "You are. We're the same one." And regarding experience and the maturity it yields, he is right. At last Frederic Henry has drawn abreast of Catherine Barkley with respect to wisdom about the world. How has he done so? By participating in love and war, and by making the hard choices that both demand.
When he walks out of the hospital at novel's end, Lieutenant Frederic Henry is a different man than he was at the opening of A Farewell to Arms. He has caught up to Catherine Barkley and now understands the world and his place in it. Sadly, he carries that understanding into the rain alone and broken, and forever without her.
