consider the merit of the prelude as a spritual autobiography

This question is relatively complicated, but you can be sure that since most of the books of "The Prelude" were developed during most of his lifetime. It is reasonable to assume that as one describes the course of one's life, one would also describe one's spiritual development. There is so much to be said about this topic that one cannot cover it in such a short space, but start with the idea that a lifetime of writing would document more than the day-to-day developments of one's life.