Remember, parents, if you expect too much from your kids, you might lead them on a path to embracing eldritch god entities and rebuilding their souls with foreign material.
From what I gather his side of the deal makes him an intermediary of a Lovecraftian God. He sees things filtered like he has high SEN while the Outer God can use him to spread his eldritch knowledge. Not that we know the reason if it's to invade or increase his own power like sowing and reaping.
His writing also seems to be affected as ''Inky'' says he is fulfilling his side of the deal by spreading his own books, which contributes to the idea the god is benefiting from that knowledge spreading. Our protagonist's social ability works for the best and the Outer God likely analyzes as well what the clients need and can use.