Responses
Most likely archangel Gabriel, since this story had religious imaginary everywhere.
I think he's just meant to be a random character that exists to give way to the story's format and some of its themes—like you said, I definitely feel as though the letter is a way for Theo to confess, but also to show the mentality of Theo at the end of the story and the way he's given into the situation and accepted it
I’m still not understanding who Gabriel is. Is Gabriel supposed to be a forgiving entity like the archangel? I don’t think Gabriel is his actual brother but he might be who Theo prayed to often? Maybe he felt writing a letter was a better way of confessing since he couldn’t actually take his confession to a priest.