Oomoto-kyo is a modern religion founded by Deguchi Nao and her husband Deguchi Onisaburo in the late 1800s. It is kind of an international form of Shintoism, which is a benign indigenous Japanese religion with roots in nature.
O-sensei was deeply involved in Oomoto-kyo and close to the founders. Saito-sensei told me how O-sensei would start praying in front of the Aikido shrine in Iwama every morning in a very loud voice starting at 5AM and wake up the people in the neighborhood. But nobody complained.
One day Saito-sensei passed on something that O-sensei told him. O-sensei believed that his devout practice of Oomoto-kyo guided him to perfect Aikido as a system of physical training by which its practitioners could improve and cleanse themselves and move toward spiritual enlightenment (satori). O-sensei said that although he was deeply religious himself, his students didn't have to be. The path was built into the Aikido movements which are in harmony with nature.
Aside from this, Saito-sensei rarely spoke of religion. However, Oomoto-kyo wasn't entirely absent in Iwama. On the 14th of every month and the 29th of April every year we would hold a ceremony in the shrine. Sometimes it was conducted by a Shinto priest. They would pass out little Oomoto-kyo prayer books and everybody would read the prayers together.
The prayers were very esoteric and I didn't understand a word of them, but I always pretended to follow along. Even though I didn't understand the words, the atmosphere was very spiritual and helped me get closer to the spirit of O-sensei's Aikido.
Fundamental principles of Oomoto-kyo are peace and world harmony. O-sensei embodied these principles completely, as did Saito-sensei.
Unfortunately, due to big egos and desires for power, Aikido became riddled with politics. But it was never like that in Iwama during the ten years I was there.
Saito-sensei was our patriarch and we followed him and his example gladly. We trained (and partied) very hard, but always had warm feelings for each other. There was never any conflict or political games of any kind.
I believe that this was a golden age in Iwama in harmony with the spirit of O-sensei's Aikido (as well as Oomoto-kyo), and I am very grateful to have had the opportunity to experience it.