As Christianity in its beginnings was surrounded by the polytheistic beliefs and practices of the pagan world, a clear and authoritative expression of Monotheism was necessary. Hence the symbols of faith, or creeds, open with the words: "I [we] believe in God"...(APOSTLES' CREED; ATHANASIAN CREED:;; NICENE CREED.)
It's important to remember that Thomas Huxley recognized Socrates as the first agnostic. Socrates very much believed in a God , although his deity was somewhat vague and outside of his people's polytheistic religion. Philosophically Socrates was the very essence of agnosticism .