Sources of revelation
All Christians consider the Bible to a be a source of revelation. Protestants consider the Bible to be the only source of revelation, while Catholics and Orthodox believe that "Tradition," or unwritten revelation passed on and explained by the Church, is also a source of revelation. However, the most crucial Christian revelation is found in the Bible.
Not all knowledge of God is due to revelation. For example, the existence of God can be concluded naturally through human reasoning. But crucial Christian doctrines like the Trinity can only be learned supernaturally, through revelation.