Objection 1: It seems that the Church should in all cases receive back those who return from heresy. For it is written (Jeremiah 3:1) in the person of the Lord: “You have prostituted yourself with many lovers; yet return to Me, says the Lord.” Now, the judgment of the Church is God’s judgment, according to Deuteronomy 1:17: “You shall hear the small as well as the great: you shall not respect the person of any man, for the judgment is God’s.” Therefore, even those guilty of the prostitution of unbelief, which is spiritual prostitution, should nevertheless be received.
Objection 2: Further, our Lord commanded Peter (Matthew 18:22) to forgive his sinning brother “not” only “seven times, but seventy times seven times,” which Jerome interprets to mean that “a man should be forgiven as often as he has sinned.” Therefore, he should be received by the Church as often as he has sinned by relapsing into heresy.
Objection 3: Further, heresy is a kind of unbelief. Now, other unbelievers who wish to convert are received by the Church. Therefore, heretics should also be received.
On the contrary, the decretal Ad abolendam (De Haereticis, cap. ix) says that “those who are found to have relapsed into the error which they had previously abjured must be handed over to the secular court.” Therefore, they should not be received by the Church.
I answer that: In obedience to the institution of our Lord, the Church extends her charity to all, not only to friends but also to enemies who persecute her, according to Matthew 5:44: “Love your enemies; do good to those who hate you.” Now, it is part of charity that we should both desire and effect the good of our neighbor. Again, good is twofold: one is spiritual, namely the salvation of the soul, which is chiefly the object of charity, since this is what we should chiefly desire for one another. Consequently, from this standpoint, heretics who return after falling, no matter how often, are admitted by the Church to penance, by which the way of salvation is opened to them. The other good is that which charity considers secondarily, namely temporal good, such as bodily life, worldly possessions, good reputation, ecclesiastical or secular dignity, for we are not bound by charity to desire this good for others except in relation to their eternal salvation and that of others. Therefore, if the possession of any of these goods by an individual could be an obstacle to the eternal salvation of many, we are not bound by charity to desire such a good for that person; rather, we should wish that they be without it, both because eternal salvation takes precedence over temporal good, and because the good of the many is to be preferred to the good of the individual. Now, if heretics were always received on their return in order to save their lives and other temporal goods, this could be detrimental to the salvation of others, both because they might infect others if they relapsed again, and because, if they escaped punishment, others would feel more secure in falling into heresy. For it is written (Ecclesiastes 8:11): “Because sentence against an evil deed is not executed speedily, the hearts of the sons of men are fully set to do evil.” For this reason, the Church not only admits to penance those who return from heresy for the first time, but also protects their lives and sometimes, by dispensation, restores them to ecclesiastical dignities they may have previously held, if their conversion appears sincere: we read that this was often done for the sake of peace. But if they fall again after being received, this seems to prove that they are unstable in faith; therefore, if they return again, they are indeed admitted to penance, but are not spared the death penalty.
Reply to Objection 1: Before God’s judgment, those who return are always received, because God is the searcher of hearts and knows those who return in sincerity. But the Church cannot imitate God in this, for she suspects that those who relapse after once being received are not sincere in their return; therefore, she does not bar them from the way of salvation, but neither does she protect them from the death sentence.
Reply to Objection 2: Our Lord spoke to Peter of sins committed against oneself, for such offenses should always be forgiven and our brother spared if he repents. These words are not to be applied to sins committed against one’s neighbor or against God, for it is not in our power to forgive such offenses, as Jerome says on Matthew 18:15: “If your brother sins against you.” Yet even in this matter, the law prescribes limits, according as God’s honor or our neighbor’s welfare demands.
Reply to Objection 3: When other unbelievers who have never received the faith are converted, they show no sign of instability in faith, as relapsed heretics do; therefore, the comparison does not hold.
Source: Summa Theologiae, Second Part of the Second Part, Question 11, Article 4