Both my sons were raised to be critical thinkers, to question, to research using reputable sites & citations & to be able to lay out a well founded arguement based on fact. They were both exposed to religion & going to church. They both became agnostics in their teens & only more skeptical as they have grown older (both now in their 30s).

If they started to gravitate to religion, those would be interesting conversations.

Everynbody learns in their own way. However, is there any chance he might be becoming schizophrenic, or have other problems? Tread carefully, but remain aware!

Tell him to read/study that book , after that he can make up his mind