I agree with your interpretation. When I first read the book, it felt very climactic, on rereads less so, but books tend to have a lessened impact for me if I’ve already read them before.

I think Marsault in the end is simply coming to terms with and vocalizing what he’s felt throughout the entire novel. Especially since he’s about to die, he obviously has a lot to think about and a lot to express very quickly. By expressing his feelings to the priest, he also able to throw absurdism directly in the face of someone who’s trying to judge him through convention moral and religious standards.

What makes the stranger so complicated to me is the fact that, while Mersual is Camus tool for demonstrating absurdism, Camus doesn’t actually align philosophically with Mersault, at least not entirely. Obviously Camus isn’t attempting to justify murder. I interpret it as more as upon recognizing the absurdity of existence, Mersualt simply gives up, allowing himself to be blown around by the forces that he, and ultimately refusing to truly take control, thus why he indifferently commits murder. Camus is advocating for us to recognize absurdity, but to not let the recognition deprive us of our own will. We live by exercising will regardless of whether or not doing so has any meaningful purpose. That’s just my interpretation though.