Without a background in Shinto, Oomoto-kyo, and Buddhism it is difficult to understand the philosophical and spiritual ideas that O'Sensei based his martial studies on. I am beginning to work on a paper to accompany an upcoming test and find that the further I go, the more there is to understand.
Several decades ago, I had read Thomas Merton's Zen and the Birds of Appetite. That served as a personal stepping stone into Buddhism. I read a lot, meditated a little, and got an appreciation for Zen while lacking the discipline to truly practice zazen.
Now it comes around again. I was reading about Oomoto-kyo. To even find a starting point, I am now reading about Shinto. I'm not going to say I understand any of it, just that I am reading about it and piecing together the major concepts and practices as a window I can look through at some of O'Sensei's writings and quotes.