What does Romans 2:4 mean?

This verse contains a crucial teaching about God's kindness. Paul is addressing anyone who doesn't think themselves guilty of the kinds of sin described in Romans 1, leading them to a judgmental attitude. Paul has stated emphatically in the previous verse that these people, actually all people, deserve the judgment of God for our sins.

Who could possibly think they would be excluded from God's judgment for sin? Some Gentiles—non-Jewish people—of Paul's day followed a philosophy of morality. Paul likely had in mind, however, the religious Jews who assumed their special national relationship with God exempted them from His judgment for personal sinfulness. This allowed them to be both judgmental about "sinful Gentiles" and complacent about their own sins.

Paul now calls this attitude presumptuous. These self-righteous sinners are presuming on or showing contempt for the riches of God's kindness, forbearance, and patience. Aware of God's vast goodness, they have miscalculated that He won't ever judge their sin, even though He may judge the sins of others. In the following verse, Paul will describe just how wrong and dangerous it is to ignore God's merciful warnings. For now, though, he says something fascinating: God's kindness is meant to bring sinners, all of us, to repentance.

In modern English, we sometimes hear the phrase "do not mistake my kindness for weakness." The same is true with God. His mercy in dealing with mankind is not a sign of indifference or frailty. It's meant to inspire us to thankfulness, to faith, and to repentance. God's temporary display of patience isn't a signal that our sin doesn't matter to Him, or that He is unwilling to express His wrath. Instead, He means to call us, through His display of kindness in this moment, to turn from our sin and follow after Him forever. That's true repentance.