Future story

"light cannot exist without darkness" this phrase always stayed in Tyr's mind, and as he grew up, it would have fueled his doubts and pushed him to doubt the religion everyone beloved in, so one day while he was, as always, skipping the group prayers, he saw some suspicious people in black robes, and followed them in the sewers, only to find out that they were demonic cultists. in the heat of the moment he stole their book, but right as he touched it, what are those memories?! my past life? another world?! It seems that I have been reincarnated. I'll focus on my other novels first