Comparison between the apostles and Novatians. The fitness of the words, “You know not what spirit you are of,” when applied to them. The desire of penance is extinguished by them when they take away its fruit. And thus are sinners deprived of the promises of Christ, though, indeed, they ought not to be too soon admitted to the mysteries. Some examples of repentance.
87. Inasmuch, then, as the Apostle forgave sins, by what authority do you say that they are not to be forgiven? Who has the most reverence for Christ, Paul or Novatian? But Paul knew that the Lord was merciful. He knew that the Lord Jesus was offended more by the harshness of the disciples than by their pitifulness.
88. Furthermore, Jesus rebuked James and John when they spoke of bringing down fire from heaven to consume those who refused to receive the Lord, and said to them: “You know not whose spirit you are of; for the Son of Man is not come to destroy men's lives but to save them.” To them, indeed, He said, “You know not whose spirit you are of,” who were of His spirit; but to you He says, “You are not of My spirit, who hold not fast My clemency, who reject My mercy, who refuse repentance which I willed to be preached by the apostles in My Name.”
89. For it is in vain that you say that you preach repentance who remove the fruits of repentance. For men are led to the pursuit of anything either by rewards or results, and every pursuit grows slack by delay. And for this reason the Lord, in order that the devotion of His disciples might be increased, said that every one who had left all that was his, and followed God, should receive sevenfold more both here and hereafter. First of all He promised the reward here, to do away with the tedium of delay, and again hereafter, that we might learn to believe that rewards will also be given to us hereafter. Present rewards are then an earnest of those hereafter.
90. If, then, any one, having committed hidden sins, shall nevertheless diligently do penance, how shall he receive those rewards if not restored to the communion of the Church? I am willing, indeed, that the guilty man should hope for pardon, should seek it with tears and groans, should seek it with the aid of the tears of all the people, should implore forgiveness; and if communion be postponed two or three times, that he should believe that his entreaties have not been urgent enough, that he must increase his tears, must come again even in greater trouble, clasp the feet of the faithful with his arms, kiss them, wash them with tears, and not let them go, so that the Lord Jesus may say of him too: “His sins which are many are forgiven, for he loved much.”
91. I have known penitents whose countenance was furrowed with tears, their cheeks worn with constant weeping, who offered their body to be trodden under foot by all, who with faces ever pale and worn with fasting bore about in a yet living body the likeness of death.
Source: On Repentance (New Advent)