7 And God has brought us into a covenant, and agreement, and a firm bond with Him, in that we say, “as we also forgive our debtors.” He who would say it effectually, “Forgive us our debts,” must say truly, “as we also forgive our debtors.” If this which is last he either say not, or say deceitfully, the other which is first he says in vain. We say to you then especially who are approaching to Holy Baptism, from your hearts forgive everything. And ye faithful, who taking advantage of this occasion are listening to this prayer, and our exposition of it, do ye wholly and from your hearts forgive whatsoever you have against any.
Forgive it there where God sees. For sometimes a man remits with the mouth, and in the heart retains; he remits with the mouth for men's sake, and retains in the heart, as not fearing the eyes of God. But do ye remit entirely. Whatever you have retained up to these holy days, in these holy days at least remit. “The sun ought not to go down upon your wrath,” yet many suns have passed. Let then your wrath at length pass away also, now that we are celebrating the days of the great Sun, of that Sun of which Scripture says, “Unto you shall the Sun of righteousness arise with healing in His wings.” What is, “in His wings”?
In His protection. Whence it is said in the Psalms, “Keep me under the shadow of Your wings.” But as to others who in the day of judgment shall repent, but all too late, and who shall mourn, yet unavailingly, it has been foretold by Wisdom what they shall then say as they repent and groan for anguish of spirit, “What has pride profited us, or what good has riches with our vaunting brought us? All these things are passed away like a shadow.” And, “Therefore have we erred from the way of truth, and the light of righteousness has not shined unto us, and the Sun of righteousness rose not upon us.” That Sun rises upon the righteous only; but this sun which we see, God “makes,” daily “to rise upon the good and evil.” The righteous attain to the seeing of that Sun; and that Sun dwells now in our hearts by faith.
If then you are angry, let not this sun go down in your heart upon your wrath; “Let not the sun go down upon your wrath;” lest haply you be angry, and so the Sun of righteousness go down upon you, and you abide in darkness.
Source: Sermons on Selected Lessons of the New Testament (New Advent)