I’m guessing the letter to Gabriel was his suicide note (Gabriel in the Bible is a messenger of God) which could symbolise how ashamed he is of himself that he can’t face God himself.
When he comes back to paradise, it’s the first time we see him actually talking to the ghosts as normally he runs away from them. So it’s like him accepting “paradise” which I think solidified his descent into madness.
thanks for the insight!
Is it wrong for me to say I preferred Jin’s story :| no offence to tehir