The two means by which God revealed Himself to mankind were through general and special revelation. General revelation is that which may be generally known and understood by all men, regardless of their relationship with God. It includes that which can be known about God through creation (Rom. 1:20), through an inner “testimony” or reason (rational thought, cf. Ps. 19:1-6; Rom. 1:19), and through conscience (Rom. 2:15).
In contrast, special revelation is that revelation that comes from God to specific people in specific times. The primary example of special revelation is the Word of God, though it also includes other kinds of specific revelation, like direct contact or conversation with God (e.g., Ex. 34:1ff), visions and dreams (e.g., 1 Kings 3:5ff), theophanies (Ex. 40), the incarnation of Christ (Jn. 1:1ff), and prophecy (1 Cor. 14).
While both general and special revelation carry some measure of authority, they have different kinds of authority.
They both have authority to provide a moral consensus about that which is right and wrong (enabling men to establish just laws, community standards, and acceptable patterns of conduct). They also both have an ability to convict men about some measure of sin and unrighteousness (Rom. 2:15b). In fact, general revelation is enough to eternally condemn those who reject what has been revealed to them (Rom. 1:20; 2:1, 15).
However, only Scripture is able to offer a clear, definitive, and unwavering picture of sin as an affront to God and God alone (Ps. 51:4a; Rom. 3:21-23; Gal. 3:19ff; 1 Cor. 10:31). And only Scripture has the authority to point men to the specific means by which they might be redeemed from sin and to God — through Jesus Christ and Him alone (Acts 4:12; Rom. 3:24ff; Gal. 3:23ff).
In other words, general revelation is enough to help men begin to understand the existence of sin and the truth that they are sinners, but only the specific revelation of God will lead men to comprehend the depth of their sin and the uniqueness of Christ to save them and transform them into the likeness of Christ. General revelation is inadequate to provide transformation into the likeness of Christ.