Concerning the the development of theism in general (I'm a Christian but I'll try to maintain a neutral POV) it could be seen as an inset desire for one to seek someone or something greater than himself. Most ancient religions are polytheistic, with monotheism being a (relatively) recent phenomenon, primarily with Judaism and later on, secondary Abrahamic religions such as Christianity and Islam, as well as Zoroastrianism.

When it comes to the Christianity-related part of your question, it seems to be all over the place so some clarification may be needed. But concerning the canonization of early Christianity, Roman Emperor Constantine organized the First Council of Nicaea in A.D. 325, where it established an "official" statement of the beliefs of Christianity (known as the Nicene Creed), and addressed certain heresies that had been developing, though for the most part the different churches were united in their religious beliefs, just not with an "official" statement of them.