In this verse Paul explained why Gentiles need to hear the gospel and experience salvation.
God has revealed His wrath as well as His righteousness (v. 17) from heaven in the gospel.39As Paul would explain, the unfolding of history also reveals God's hatred toward sin and His judgment of sin. The moral devolution of mankind is not just a natural consequence of man's sinning but also a result of God's judgment of sinners. The final judgment of sin will occur in the eschaton (end times), but already God is pouring out His wrath against sin to a lesser degree (cf. Eph. 5:6; Col. 3:6). Paul described wrath as revealed from heaven because it comes from God who is in heaven.40
"God's wrath is his divine displeasure with sin. We call it wrath' because it shares certain basic characteristics of human wrath. But because it is God's wrath it can have none of the sinful qualities of its analogical counterpart."41
"Ungodliness"means lack of reverence for God. Man's neglect of God and rebellion against God are evidences of ungodliness. "Unrighteousness"or "wickedness"(NIV) means injustice toward other human beings. We see it in any attitude or action that is unloving. Together these two words show humankind's failure to love God and other people as we should (Deut. 6:5; Lev. 19:18; Matt. 22:37-39). Verses 19-27 demonstrate man's ungodliness, and verses 28-32 show his wickedness.
The "truth"refers to truth that people know about God (cf. v. 25). They suppress this truth by their wickedness.
". . . whenever the truth starts to exert itself and makes them feel uneasy in their moral nature, they hold it down, suppress it. Some drown its voice by rushing on into their immoralities; others strangle the disturbing voice by argument and by denial."42
