Religion is the spiritual belief in a higher power in an organzied form. Simply believing in someting is not religious, but joining or establishing a faith with many followers is. A monotheistic religion is the belief in only one god. The three major monotheistic religions are Christianity, Judaism, and Islam. All three religions are similar in their belief in god, but differ in culture, holy books, and who they believed to be the true prophet. Polytheism is a religion in which there are many gods.