That particular phrase was first highlighted for me 30 years ago when I began my novitiate in August of 1979. Fr. Joseph Peters O.S.B., who gave me some retreat conferences as I began my novitiate, mentioned that phrase of the Lord’s Prayer as one which his mother gave special emphasis to when he was a boy. She told him, “If you don’t mean it don’t pray it” Very sage advise. To pray that prayer really doesn’t leave room for hate and anger in your heart, or you actually end up asking the Lord for His condemnation. Not the preferred out come for most people’s prayers.
This notion that the Lord's forgiveness mirrors our willingness to forgive can be found a number of times in the New Testament.
Matthew 6:14-15 (Right after the Lord's Prayer)Some folks might have the mistaken notion that a monastery is a place full of saints. I thank God that it is not. We, like all families, present each other with numerous opportunities to practice forgiveness. I thank God each day for my brother's weaknesses because through forgiving each other we can hope for God's forgiveness.
If you forgive others their transgressions, your heavenly Father will forgive you. But if you do not forgive others, neither will your Father forgive your transgressions.
Mark 11:25
When you stand to pray, forgive anyone against whom you have a grievance, so that your heavenly Father may in turn forgive you your transgressions.
Luke 6:37
Stop judging and you will not be judged. Stop condemning and you will not be condemned. Forgive and you will be forgiven.
Colossians 3:13
Put on then, as God's chosen ones, holy and beloved, heartfelt compassion, kindness, humility, gentleness, and patience, bearing with one another and forgiving one another, if one has a grievance against another; as the Lord has forgiven you, so must you also do.
Biblical Text Source: The New American Bible