General and Special Revelation
Christianity is not based on moralisms or speculative philosophy; it is a revealed faith. But it makes a distinction between general revelation (in creation) and special revelation (in the Bible).
General revelation: the universal disclosure of God in nature, in providential history and in moral law within the heart (conscience), whereby all persons at all times and places gain a rudimentary understanding of the Creator and his moral demands. (Romans 1:18-20).
Special revelation: God’s self-disclosure in redemptive history and in the interpretive word of Scripture whereby He makes Himself and His truth known at specific times and to specific people. God cannot be known redemptively except as He reveals Himself to us. Jesus is the culmination of God's self-disclosure to man and since Jesus cannot be separated from His word, the Scriptures are the ultimate form of divine revelation from God to us, for without them, we would know nothing certain about Jesus or any of the Divine Persons of the Holy Trinity.
'Their voice has gone out to all the earth, and their words to the ends of the world'" (Rom. 10:18).
"The heavens proclaim his righteousness, and all the peoples see his glory." (Psalm 97:6)
"In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days He has spoken to us by His Son" (Hebrews 1:1-2).
Related: Knowability of God; Exclusivism vs. Inclusivism