I have a question, I don’t mind spoilers! how exactly can tes “save” the world? if n...

I'm thinking Maybe he has to kill the black hair saint as in a couple of lives she used him for her own benefits

I suppose he either has to kill the saint or kill the god who abandoned their world

It could be

Kill the old god that abandoned the world.
Kill the saintess Ailette who is trying to bring a new god into the world as its new religion.

Not a spoiler, just my theory, but I think it has something to do with the fact that the god that created this world abandoned it, so maybe by bringing a new God?

Spoiler
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The creator who made this world abandoned it, but a world cannot exist without a god, so this loop was created as a cheat to sustain it. Tes does not know this and as a supporter of the church would not even consider there being other another god lest he be labeled a heretic. This is where Ailette comes in by establishing a church for the Voice that Shapes the World so the god can gain more power to support this universe as the god gains more supporters. Ailette has to do this through the storyline discreetly while sealing away Reed/EvilTes.