11 But these must fear, lest they fall into another gulf, and they die through a perverse hope, who could not die through despair. For they change their thoughts, which are far different indeed from what they were before, but not less pernicious, and begin again to say in their hearts, “If in whatever day I turn from my most evil way, the merciful God, as He truly promises by the Prophet, will forget all my iniquities, why should I turn today and not tomorrow? Let this day pass as yesterday, in excess of guilty pleasure, in the full flow of licentiousness, let it wallow in deadly delights; tomorrow I shall 'turn myself,' and there will be an end to it.”
One may answer you, An end of what? Of mine iniquities, you will say. Well, rejoice indeed, that tomorrow there will be an end of your iniquities. But what if before tomorrow your own end shall be? So then you do well indeed to rejoice that God has promised you forgiveness for your iniquities, if you are converted; but no one has promised you tomorrow. Or if perchance some astrologer has promised it, it is a far different thing from God's promise. Many have these astrologers deceived, in that they have promised themselves advantages, and have found only losses.
Therefore for the sake of these again whose hope is wrong, does the Householder go forth. As He went forth to those who had despaired wrongly, and were lost in their despair, and called them back to hope; so does He go forth to these also who would perish through an evil hope; and by another book He says to them, “Make no tarrying to turn to the Lord.” As He had said to the others, “In whatsoever day a man shall turn from his most wicked way, I will forget all his iniquities,” and took despair away from them, because they had now given up their soul to perdition, despairing of forgiveness by any means; so does He go forth to these also who have a mind to perish through hope and delay; and speaks to them, and chides them, “Make no tarrying to turn to the Lord, and put not off from day to day; for suddenly shall the wrath of the Lord come forth, and in the day of vengeance He will destroy you.”
Therefore put not off, shut not against yourself what now is open. Lo, the Giver of forgiveness opens the door to you; why do you delay? You ought to rejoice, were He to open after ever so long a time to your knocking; you have not knocked, yet does He open, and do you remain outside? Put not off then. Scripture says in a certain place, as touching works of mercy, “Say not, Go, and come again, and tomorrow I will give; when you can do the kindness at once; for you know not what may happen on the morrow.”
Here then is a precept of not putting off being merciful to another, and will you by putting off be cruel against your own self? You ought not to put off to give bread, and will you put off to receive forgiveness? If you do not put off in showing pity towards another, “pity your own soul also in pleasing God.” Give alms to your own soul also. Nay I do not say, give to it, but thrust not back His Hand that would give to you.
Source: Sermons on Selected Lessons of the New Testament (New Advent)