Romans 12:19 (KJV) Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord.

New American Standard Bible
Romans 12:19 (NAS) Never take your own revenge, beloved, but leave room for the wrath of God, for it is written, “VENGEANCE IS MINE, I WILL REPAY,” says the Lord.

Good News Translation
Romans 12:19 (GNT) Never take revenge, my friends, but instead let God’s anger do it. For the scripture says, “I will take revenge, I will pay back, says the Lord.”

Verse 21
Do not be overcome by evil, but overcome evil with good.

Romans 12:21 is a comprehensive summary of Romans 12:19-20, that is, “be not carried away to revenge and retaliation (verse 19) by evil which is committed against you, but overcome the evil by the good which you show to your enemy (verse 20), put to shame by your noble spirit, ceases to act malignantly against you and becomes your friend”.