>>509047466He didn't really repent and it was the last couple years he was alive. He lamented for having done the rituals that ended up summoning things because it brought great torment to the people around him, the areas they did them in, the people around those areas and himself personally.
There's various memoirs about this out there but it's been a long time since I read about him.
To paraphrase what I remember he was upset about soul contracts he didn't know were soul contracts and he thought it was kind of a meme doing ancient cabalist rituals in his study to measure what does and doesn't work.
Once he found out that you can't just move and the bad stuff goes away as well as the mental and spiritual drain he was sad that he played with powers outside of typical mortal control.
In a sense he was just kind of a puppet with a curiosity of esoteric morbid stuff and was bread crumbed into doing these things so other people could see what would happen so they didn't have to suffer the same way he did.
The last couple years of his life he spent a lot of time meditating away from the public but when he did go out spent most of his time around people warning them not to bind themselves to things that will consume them.