Vengeance: Avenge Not Yourselves
The greatest test of a Christian within the New Testament is how he treats his enemies. When we are wronged, we lash out in response to “defend” ourselves. We demand what is “equitable” in relationship to the harm that has been done to us. Vengeance is that demanding attitude that what was done to me ought to also be done to my enemy. Christians are directed not to harbor such thoughts in their sanctified minds. 
Romans 12:19-21 says, “Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, vengeance is mine; I will repay, saith the Lord. Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head. Be not overcome of evil, but overcome evil with good.” Peter wrote, “For even hereunto were ye called: because Christ also suffered for us, leaving us an example, that ye should follow his steps: Who did no sin, neither was guile found in his mouth: Who, when he was reviled, reviled not again; when he suffered, he threatened not; but committed himself to him that judgeth righteously” (1 Peter 2:21-23).
When pursued by our enemies, how do we respond? Do we avenge or “give place unto wrath?” Do we revile or revile not? Do we threaten or threaten not? Do render our own verdict, or commit ourselves to the righteous judge? Do overcome evil with evil or do we overcome evil with good? Our enemies deserve our mercy and love because we were once God’s enemy and that is how God looked upon us. To treat them otherwise, is to invite the same judgment that we mete out upon them upon ourselves (Matthew 7:1).