When God forgives he does so ‘in Christ’ (Eph[esians] 4:32; cf Matt[hew] 18:35).”—New Testament Commentary, Exposition of Galatians, Ephesians, Philippians, Colossians, and Philemon, by William Hendriksen, 1996, page 157.
... This could suggest that, unusually, ὁ κύριος [ho kyʹri·os, “the Lord”] here refers after all to God (the thought would then be directly parallel to that of Matt[hew] 6:12, 14-15; 18:23-35 . . .