Revelation is how God, the Creator of all things, makes himself known to us—his creatures. Without God speaking to us—in nature and in the Bible—we would have no way of knowing that he exists, who he is, what he has done to save us in Jesus Christ, or how we are to live and worship him. Theologians distinguish between two types of revelation: general and special revelation.
General revelation is God’s showing us what is true about himself through the things he has made (nature/creation). Psalm 19:1–6 and Romans 1:19–21 describe this, and Romans 2 tells us that the law of God is inscribed upon the human heart. General revelation tells us enough about God to condemn us, but not enough to save us.
Special revelation is needed for a saving knowledge of God. In special revelation, God shows us what is true about himself in his plan of redemption through his only son, Jesus Christ. This plan and the person and work of Jesus are not found anywhere in nature but in the Bible alone.
Only in the Bible are we able to learn how we are saved—and who can save us! The Bible doesn’t address every area of life or answer every question we have about God. It is intentionally limited to revealing God’s plan of redemption. We need both general and special revelation for life; however, we cannot do without the latter for eternal life.