One of the foundational truths for the Christian life, faith, and worldview is that God has spoken to humans and that we know what he has said. In some ways, the Christian understands God to be speaking to every human of every nationality all the time, whether they are living or dead, Christian or pagan. But it is helpful to distinguish between the various methods God uses to communicate to humans, that is, it is helpful to observe that there are categories of revelation.
The broadest form of communication God uses is general revelation. It is general both in audience and in content. Every human being is audience to what God says in general revelation. Romans 1 and 2 are key here because they bring out both the source and (at least by implication) content of this revelation. The source of God’s general revelation is “what has been made” (1:20). We know from experience that everything an artist makes tells us about the artist’s personality. This observation holds true for the Creator of the universe as well. God shows his eternal power and genuine deity through what he has made.
In Romans 1:32 and in chapter 2, Paul brings out a specific category of creation, man’s inner awareness of moral obligation to God. After listing off a litany of sins like homosexuality (1:26–27) and disobedience to parents (1:30), Paul says that unregenerate people “know God's righteous decree that those who do such things deserve death.” Romans 2:15 mentions the specific faculty at work here, the “conscience” which works like a law written on the heart of those who did not receive the Mosaic Law.
What must be pointed out is that man is not the origin of this law. He is not the measure of all things and his conscience is not the product of blind chance or human ingenuity. His conscience was built in by the Creator. That's what makes it revelation. They are common to all humankind. That's what makes it general revelation.
But this revelation is also general in its content. Although the analogy is probably too crude for anything other than a blog, general revelation gives fallen humans just enough rope to hang themselves. Paul says it more appropriately: “his eternal power and divine nature-- have been clearly seen, being understood from what has been made, so that men are without excuse” (1:20). General revelation does contain enough to condemn all who do not glorify God as God and thank him. It renders them “without excuse.”
But much has been left unsaid by general revelation. For instance, Christ alone reveals the only deliverance from sin’s penalty and power. So God has told us more than merely what he reveals in his creation. He has given to some more specific, that is, special revelation. I’ll be writing about that one next time.