SPOILER: What did the final lines mean?

It seems it's about this man losing/reducing his years (decades?) of coldness and cynicism because that's his reaction to the ugliness of reality. The suffering and maliciousness that he's surrounded by for which he see's religion/faith/god as a cowardly or delusional response too.

So in the end, he recognizes he was wrong at least partially, to make this sweeping and simplistic judgement about the innocence of children. To be ignorant and unaware of the potential horrors and pain of humanity that they'll encounter in adulthood.

Or something lol.

I doubt he is someone who will ever find faith in a religion or believe in a personal god but perhaps he'll find some non-religious faith in the goodness of humanity and maybe even some spirituality.

I took it to mean that he realizes that we need to value precious things and precious moments, even though the world can be so ugly. That perhaps those moments of joy are all we have (because hope is deceptive, and god may not exist, and life often sucks), but that doesn't mean that they should not be fully lived and appreciated while they last, and for what they are.