Commentaries:
At the very least, Paul derived this from the example of Christ, who submitted to wicked and corrupt officials and authorities. Jesus had every right to rebel. He was completely innocent and had done nothing wrong—nothing of which He was accused had been part of His conduct. However, He had every intention of doing the right thing, and He carried through with it.
The true Christian consciously chooses to suffer evil rather than do evil because it would be wrong to do anything other than what Christ did. He set the example. He is the archetype; He is the One who goes before. The Christian is not a masochist, but by faith, he takes steps to prevent war. He does this because he recognizes that two wrongs do not make a right. Just because someone abuses authority does not give him the right from God to fail to submit to it. This is why there is never any real thought to war. Somebody gets into power and abuses his authority, and those who are under him react carnally and retaliate to get back at the one in authority—and the cycle never ends!
Will there ever be peace? There will be peace when people submit to God, and that means submitting to His way. If everybody would submit to God's way, war would stop overnight—that would be the end! But men will not submit to God (Romans 8:7). A major principle we are to learn in this life is to submit under duress, under abuse—when the pressure is on and the desire to retaliate is strongest. We have to learn not to justify our retaliation by saying, "He made me do it—the Devil made me do it!" All the ways of man are right in his own eyes (Proverbs 14:12).
John W. Ritenbaugh
Submitting (Part 1)
God alone has the wisdom and power and the right to take vengeance. Regarding war, Exodus 14:14 says, "The LORD will fight for you." War has never solved man's problems, and God promises that those who live by violence will die by it (Matthew 26:52). Christians must treat others with kindness, gentleness, and love (Luke 6:31; Galatians 5:14-15).
Martin G. Collins
The Sixth Commandment
Self-restraint and obedience to God's law is realized in outgoing concern for others that exceeds and rules over our own self-interest. Even lawful acts may on occasion cause other brethren to stumble or be made weak. Self-control provides the ability to resist what may cause pain to others. Thus, we exercise self-control for others, as well as for ourselves.
Martin G. Collins
Self-Control
These remarkably high standards are possible because God is our strength. He works unseen to human eyes and makes living according to these standards possible.
Deuteronomy 32:35-37 is the source for Paul's instruction. God demands this apparently passive requirement of us as an act of faith in our intensely close relationship with Him. It may seem as if a Christian who submits to God's instruction is spineless and easily intimidated, but in God's judgment, he is strong where it really matters: in faith. The Christian, like Christ, has committed himself to the One who judges righteously, who will act in due time, using His powers in love toward all concerned (I Peter 2:23). When a person in a situation like this uses his natural powers to retaliate, he invariably does more damage than good.
Because our God is all-powerful, we must grow to trust Him, understanding that His judgment will be exactly right because He is not only there, He is also powerful in wisdom and mercy. This measure of faith enabled Abraham to trust God to raise Isaac should he actually be sacrificially slain.
John W. Ritenbaugh
Power Belongs to God (Part One)
Other Forerunner Commentary entries containing Romans 12:21:
Genesis 6:5
Exodus 20:13
Jeremiah 29:7
Luke 21:36
Romans 13:1
James 1:12
1 Peter 2:21-23
Revelation 6:10