Titus of Bostra — as excerpted in the Catena Aurea on Luke 11:1-4

“(in Matt.) This also was necessarily added, for no one is found without sin, that we should not be hindered from the holy participation on account of man’s guilt. For whereas we are bound to render unto Christ all manner of holiness, who maketh His Spirit to dwell in us, we are to be blamed if we keep not our temples clean for Him. But this defect is supplied by the goodness of God, remitting to human frailty the severe punishment of sin. And this act is done justly by the just God, when we forgive as it were our debtors, those, namely, who have injured us, and have not restored what was due. Hence it follows, For we also forgive every one that is indebted to us.”