In accordance with your hardness and your impenitent heart you are treasuring up for yourself wrath in the day of wrath and the righteous judgment of God, who will render to each one according to his deeds.
A self-righteous person bypasses the “riches” of God’s goodness, forbearance and long-suffering. He does not allow them to lead him to repentance. Instead, he amasses for himself another kind of riches. The Greek word for “treasures” in the original signifies not only the amassing of a treasure, but also its safekeeping.
What impenitent man amasses is the opposite of goodness: it is wrath. It is a matter of God’s wrath (ch1, v.18), but it is man himself who piles up that wrath through “his deeds”, his various sins.
This clearly shows what God’s wrath consists in: not fury or resentment that God may entertain towards His creature, but holy, righteous anger that cannot simply tolerate mankind’s sins. God’s wrath is nothing other than the response of His righteousness regarding sin.
This wrath is being amassed now. But everyone is still able to take refuge in Christ, who “delivers us from the wrath to come” (1 Thessalonians 1:10). Whoever refuses salvation in Christ will suffer wrath “in the day of wrath and the righteous judgment of God”. Then it will be clear that there is just retribution for every evil deed on earth. Nothing will have been forgotten. “And the dead were judged according to their works by the things which were written in the books” (Revelation 20:12).