What a good way to put it..much like the idea of having many lives,is that in the Hindu religion,that one keeps on being reincarnated, and struggling for something, who knows what,maybe the top of the Tower..Ms. Mod hit it spot on. Roland is on another turn, another try for the Tower. I get the sense that some events in each turn are like Keystone Earth--they are foundational and have to happen each turn. Others are modified by decisions made at the last turn of the wheel.
I liked the movie a lot, and have watched it several times.