10 Having then these examples, let us be sober, and let us strive not to despond, and if at any time we fall, not to lie prostrate. For not to cast you into slothfulness, did I speak of the sins of David, but to work in you more fear. For if that righteous man through a little remissness received such wounds, what shall we have to suffer, who are every day negligent? Do not therefore look at his fall, and be remiss, but consider what great things he did even after this, what great mournings, how much repentance he showed forth, adding his nights to his days, pouring forth fountains of tears, washing his couch with his tears, withal clothing himself in sackcloth.
Now if he needed so great a conversion, when will it be possible for us to be saved, feeling insensible after so many sins? For he that has many good deeds, would easily even by this throw a shade over his sins; but he that is unarmed, wherever he may receive a dart, receives a mortal wound.
In order therefore that this may not be so, let us arm ourselves with good works; and if any offense have befallen us, let us wash it away: that we may be counted worthy, after having lived the present life to the glory of God, to enjoy the life to come; unto which may we all attain, by the grace and love towards man of our Lord Jesus Christ, to whom be glory and might forever and ever. Amen.
Source: Homilies on the Gospel of St. Matthew (New Advent)