The Bible is part of religion/s/, not what created the religion/s/. They already had the beliefs, same way as I have teachings that many don't, have heard them, they aren't in the Bible, are they therefore not part of ''religious'' beliefs? hmm
Look at Judaism, the have a verbal Torah, that is very important, and as authoritative as the written Torah, (afaik). Xianity comes from a similar tradition/background as Judaism, and the same idea applies.
That is why Xians can have set beliefs that are not explicitly stated in the Bible, yet the Bible traditionally is said to back the beliefs up!
There is disagreement between Xian groups, but this is because Xianity formed in different areas, and among different groups/
This, however, does not change the fact that the religious text, if understood properly, is exactly correct, it merely means there is disagreement on what the text means.