Probably the least talked about and least popular characteristic of God, His wrath. It's important to understand His wrath, though, in order to better understand His mercy.
Definitions range of "resentful displeasure" to "deep, intense anger and indignation." Based on a passage in Romans 2 I'm likely to go towards the "deep, intense anger" side. "...For a day of anger is coming, when God's righteous judgment will be revealed. He will judge everyone according to what they have done. He will give eternal life to those who keep on doing good, seeking after the glory and honor and immortality that God offers. But he will pour out his anger and wrath on those who live for themselves, who refuse to obey the truth and instead live lives of wickedness." (Romans 2:5-8) One may wonder how this can come from a God whose name also is "Love" (I John 4:8).
J.I. Packer writes, "God is only angry where anger is called for. Would a God who did not react adversely to evil in His world be morally perfect? Surely not. It is this adverse reaction to evil, which is a necessary part of moral perfection, that the Bible has in view when it speaks of God's wrath." The thing is, wrath is a characteristic of God. He is holy. All of us on this earth are not. When holiness sees unholiness there's deep, intense tension. God wants to rid us of our unholiness. This does not mean He wants to kill us all, quite the contrary. He wants to save us, ridding us of our unholiness so we can be holy in His sight.
The Bible talks about God's wrath and mercy. We have and will experience God's wrath on earth because there is evil in this world, evil even in you and me. The only time it will end is when Jesus comes back. Then mercy is promised to all, but a few. His wrath will continue to be seen by those who reject Him as God. (Matthew 12:31) That's the beauty of Jesus, the beauty of mercy. For those of us who love God and submit to Him as Lord and Savior, we may wonder why He doesn't just get rid of the evil now to spare the rest of us from His wrath. Maybe we need to revisit the parable of the wheat and weeds (Matthew 13:24-30)...