What does Romans 12:21 mean?

Romans 12 is very much a description of what it means to lead the life of a living sacrifice to God. If we're honest with ourselves, it sounds very difficult. Most of Paul's bullet-point commands in the previous verses have to do with setting ourselves aside. It's tough for us to do this for the good of our fellow Christians, let alone for our enemies. Difficult or not, Paul is calling us to live as Jesus did.

Now Paul comes to the final command of the chapter. In essence, he commands us to be strong in our conviction to live in this way. We are not to be overcome by evil, but to overcome evil with good. Paul seems to have in mind the idea that we are overcome by evil when we join in and give it back, when we sink to evil's level. That just results in more sin, more pain, and an endless cycle of revenge and hatred.

In other words, evil wins when we live first for ourselves, our rights, and our own good, instead of the good of others.

If we are strong in Christ, however, we have a great opportunity to overcome evil by continuing to do Christlike good. Evil won't be annihilated from the world on this side of eternity. That ultimate victory over evil is scheduled for some day in the future, at the hands of God (Revelation 20:11–15). All the same, evil can be defeated any time Christians stand up and give back good to those who do wrong to them. Evil struggles to stand against courageous and sacrificial love.

Paul will continue this thought in the next verses as he transitions to the relationship between Christians and earthly government.