Before Paul develops the theme of the gospel, he says that the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men (v. 18a). It is perfectly appropriate for a holy and righteous God to be moved to anger against evil. A judge with no distaste for evil would not be a good judge. God is angry with two distinct things: ungodliness, or irreverence or impiety (from the Latin word impiatos), and unrighteousness. Ungodliness and unrighteousness are vast generic terms that cover a multitude of sins, but Paul is not talking about a multitude of sins here. He has in view one particular sin. It is a universal sin, one committed by every human being. It is the sin that most clearly expresses our Adamic nature, our corruption and fallenness in the flesh. Paul does not leave us to guess at the nature of this sin; God is provoked to an orgy of anger against the sin of those who suppress the truth in unrighteousness (v. 18b). The single sin that provokes God’s wrath against the whole human race is the sin of suppressing truth.
The root of the Greek word translated suppress is katacain, which can also be translated as to hinder, to stifle, to incarcerate, to put in detention, to obscure, or to repress. We might think of a gigantic spring or coil that would require all the strength in our body to push down or compress. While we are pushing it down, it is resisting our strength and seeking to spring back up and recoil into its original position. By nature we take the truth of God and press it down. We force it into our subconscious, as it were, to get it out of our mind; yet despite all the strength we use to suppress it, we simply cannot eradicate it. We cannot get rid of it because it is always and everywhere pushing back up. The specific sin here is the suppression of truth.
What truth is being suppressed? Paul tells us: because what may be known of God is manifest in them, for God has shown it to them (v. 19). The truth that every human being suppresses is the truth of God, what God reveals of Himself in nature to the whole human race. This is not the truth of God that we learn through the Bible. We suppress that, too, but here Paul is writing of a truth that is known about God apart from the Bible, a knowledge of God that God makes manifest. The Greek word is phoneros, which means “to show plainly.” We use the term phenomenon, which is derived from that Greek word. The Latin text translates it as manifestum. The knowledge that God gives of Himself is not obscure. It is not buried with hidden clues that only an intellectual, elite group of people are able to discover after a painful and tedious search of sifting through the evidence. The truth that God gives of Himself is manifest. It is clear—so plain that it is clear to everybody.
Application
As you pray today, praise God for His holy and righteous wrath against evil and for His goodness in delivering you from His wrath. Believing on Christ, you can know that He died on the cross as an acceptable sacrifice for your sins. In our justification, He has given us His righteousness—even we who once suppressed the truth in unrighteousness. Let us all the more in light of God’s love proclaim it.
R.C. Sproul The Power of the Gospel