17-21 Paul takes his stand alongside believers by giving them explicit counsel about how to face the hostile world. "Do not repay evil for evil" (v.17), for to do so would be to follow the inclination of the sinful human nature. The remainder of v.17 means that believers are constantly under the scrutiny of unsaved people as well as of fellow Christians, and they must be careful that their conduct does not betray the high standards of the Gospel (cf. Col 4:5; 1 Tim 3:7). Each situation that holds prospect for a witness to the world should be weighed so that the action taken will not bring unfavorable reflection on the Gospel.
The charge to "live at peace with everyone" is hedged about with two qualifying statements. "If it be possible" suggests that there are instances in human relations when the strongest desire for concord will not avail. If disharmony and conflict should come, however, we should accept the responsibility for resolving it. Believers may not be able to persuade the other party, but they can at least refuse to be the instigator of trouble. God wants us to be peacemakers (Matt 5:9).
This peace-loving attitude may be costly, however, because some will want to take advantage of it, figuring that Christian principles will not permit the wronged party to retaliate. In such a case, what is to be done? The path of duty is clear: We are not to take vengeance, for vengeance trespasses on the province of God, the great Judge of all. We must "leave room for God's wrath" (v.19), trusting that he will take care of the situation. He will not be too lenient or too severe. Here Paul quotes Duet 32:35, whose context indicates that the Lord will intervene to vindicate his people when their enemies abuse them and gloat over them.
Paul does not suggest that God's wrath will be visited on the wrongdoer immediately. On the contrary, the hope is that those who have perpetrated the wrong will have a change of heart, will be convicted of their sin, and will be won over by refusal of the Christian to retaliate (v.20). Here again Paul lets the OT speak for him (Prov 25:21-22). "Burning coals" are best understood as the burning pangs of shame and guilt. There is, of course, no definite promise at this point that offenders will be converted. By going the second mile and showing and showing unexpected kindness, believers may also spare their companions from having the same experience. In that measure. society has benefited.
Guidance on the problem of coping with evil reaches its climax in the final admonition: "Do not be overcome by evil, but overcome evil with good" (v.21). Being overcome by evil means to give in to the temptation to meet evil with evil, to retaliate. To overcome evil with good has been illustrated in v.20. The world's philosophy leads people to expect retaliation when they have wronged another. To receive kindness, to see love when it seems uncalled for, can melt the hardest heart.
[NIV BIBLE COMMENTARY Volume 2: New Testament].
JESUS IS LORD.