Hebrews 7:8-10
Let us become clean to the utmost of our power. Let us wipe away our sins. And how to wipe them away, the prophet teaches, saying, “Wash you, make you clean, put away your wickedness from your souls, before My eyes.” What is “before My eyes”? Because some seem to be free from wickedness, but only to men, while to God they are manifest as being “whited sepulchers.” Therefore He says, so put them away as I see. “Learn to do well, seek judgment, do justice for the poor and lowly.” “Come now, and let us reason together, says the Lord: and though your sins be as scarlet, I will make you white as snow, and if they be as crimson, I will make you white as wool.” You see that we must first cleanse ourselves, and then God cleanses us. For having said first, “Wash you, make you clean,” He then added “I will make you white.”
Let no one then, [even] of those who have come to the extremest wickedness, despair of himself. For (He says) even if you have passed into the habit, yea and almost into the nature of wickedness itself, be not afraid. Therefore taking [the instance of] colors that are not superficial but almost of the substance of the materials, He said that He would bring them into the opposite state. For He did not simply say that He would “wash” us, but that He would “make” us “white, as snow and as wool,” in order to hold out good hopes before us. Great then is the power of repentance, at least if it makes us as snow, and whitens us as wool, even if sin have first got possession and dyed our souls.
Let us labor earnestly then to become clean; He has enjoined nothing burdensome. “Judge the fatherless, and do justice for the widow.” You see everywhere how great account God makes of mercy, and of standing forward in behalf of those that are wronged. These good deeds let us pursue after, and we shall be able also, by the grace of God, to attain to the blessings to come: which may we all be counted worthy of, in Christ Jesus our Lord, with whom to the Father together with the Holy Ghost, be glory, power, honor, now and for ever and world without end. Amen.
Source: Homilies on the Epistle to the Hebrews (New Advent)