It is quite straightforward:
- heaven is unknowable because it is hidden and no one came back to tell
- if! God exists then maybe the revelation is true after all, in which case,
- the underlying message of the revelation in all its forms it is how to get back, as you are wanted back
Also the last sentence is meant, I think, to make one see the waste of energy religious ritual became and the uselessly intricate creatures belief based behaviors make people.