I have no idea wtf is happening with the story now... what the heck is going on?
I haven't read ahead, so there are no spoilers here, but there is a lot of my speculation.
The world seems to run on a cyclical system where a demon lord arises and is driven to cause calamity, even if they weren't particularly evil before. The god of reincarnation is tasked with ensuring that warriors strong enough to fight the demon lord exist during each cycle.
Something went wrong in the last cycle, and the world was nearly destroyed because the god responsible was doing something to endanger the cycle. That god was dismissed and the current goddess took over.
The current enemies are the product of the previous god's abuse of power, being people reincarnated into their own world. What their overall goal is remains a mystery beyond defeating the goddess and bringing their master back.