The second half of verse 12 is explained by Christ in these two verses, but the explanation is delayed until the prayer is finished so as not to interrupt it. This is the only petition that is commented on by the Lord, and which has a condition attached to it.
We may use our awareness that we have forgiven others to assure ourselves that we have been pardoned by God. We ask for the forgiveness of God, confident that we will receive it because we too have shown forgiveness to others. If we are enabled to freely forgive others then it is because God’s grace and mercy has entered our hearts. The natural bitterness and desire for revenge has been taken away. If we are able to forgive in this way, how much more is God able to forgive us, for he abounds in mercy and delights to show men and women his grace. Seen this way, our forgiving others is a mark that we have also received forgiveness. The one praying who adds these words to his prayer gains confidence that God will forgive him. This counts more than riches, houses, fame, success, education; to be in a forgiven state is more marvellous than all we might gain on earth.
Should I forgive every offence committed against me? Are there any conditions to forgiveness or should it be extended to all without question? Should I withhold pardon until there has been an explicit statement of repentance? Christ forgive his enemies and he prayed for the pardon of those who nailed him to the cross while they were still railing against him (Luke 23:34). His prayer came before their repentance and yet, in answer to that prayer, many did repent only a few weeks. We too pray for those whose hearts are still hardened against us. But it is one thing to pray for a man’s repentance; it is another to offer personal forgiveness before repentance is shown. When we are talking of serious offences, there must be repentance first. However there are many minor offences which it would be over scrupulous to expect our fellow Christians to solemnly repent of each time.
How do I know I have forgiven another from the heart? The heart is deceitful and the flesh acts badly. Resentment may spring up within us even after we thought that we had pardoned someone. In this situation we are to remind ourselves that we have already forgiven the person and to pray that our natural desire for revenge may not assert itself, lest we become more guilty than the one who has offended against us. To help us freely forgive those who do us wrong, we must remind ourselves of how much the Lord has forgiven us. Our familiarity with our sins and our sense of what they deserve gives us the ability to forgive others.