On the contrary, The Apostle says (Titus 3:10, 11): "A man that is a heretic, after the first and second admonition, avoid: knowing that he, that is such an one, is subverted."
I answer that, With regard to heretics two points must be observed: one, on their own side; the other, on the side of the Church. On their own side there is the sin, whereby they deserve not only to be separated from the Church by excommunication, but also to be severed from the world by death. For it is a much graver matter to corrupt the faith which quickens the soul, than to forge money, which supports temporal life. Wherefore if forgers of money and other evil-doers are forthwith condemned to death by the secular authority, much more reason is there for heretics, as soon as they are convicted of heresy, to be not only excommunicated but even put to death.
On the part of the Church, however, there is mercy which looks to the conversion of the wanderer, wherefore she condemns not at once, but "after the first and second admonition," as the Apostle directs: after that, if he is yet stubborn, the Church no longer hoping for his conversion, looks to the salvation of others, by excommunicating him and separating him from the Church, and furthermore delivers him to the secular tribunal to be exterminated thereby from the world by death. For Jerome commenting on Gal. 5:9, "A little leaven," says: "Cut off the decayed flesh, expel the mangy sheep from the fold, lest the whole house, the whole paste, the whole body, the whole flock, burn, perish, rot, die. Arius was but one spark in Alexandria, but as that spark was not at once put out, the whole earth was laid waste by its flame."
Reply Obj. 1: This very modesty demands that the heretic should be admonished a first and second time: and if he be unwilling to retract, he must be reckoned as already "subverted," as we may gather from the words of the Apostle quoted above.
Reply Obj. 2: The profit that ensues from heresy is beside the intention of heretics, for it consists in the constancy of the faithful being put to the test, and "makes us shake off our sluggishness, and search the Scriptures more carefully," as Augustine states (De Gen. cont. Manich. i, 1). What they really intend is the corruption of the faith, which is to inflict very great harm indeed. Consequently we should consider what they directly intend, and expel them, rather than what is beside their intention, and so, tolerate them.
Reply Obj. 3: According to Decret. (xxiv, qu. iii, can. Notandum), "to be excommunicated is not to be uprooted." A man is excommunicated, as the Apostle says (1 Cor. 5:5) that his "spirit may be saved in the day of Our Lord." Yet if heretics be altogether uprooted by death, this is not contrary to Our Lord's command, which is to be understood as referring to the case when the cockle cannot be plucked up without plucking up the wheat, as we explained above (Q. 10, A. 8, ad 1), when treating of unbelievers in general. _______________________
FOURTH ARTICLE [II-II, Q. 11, Art. 4]
Whether the Church Should Receive Those Who Return from Heresy?
Objection 1: It would seem that the Church ought in all cases to receive those who return from heresy. For it is written (Jer. 3:1) in the person of the Lord: "Thou hast prostituted thyself to many lovers; nevertheless return to Me saith the Lord." Now the sentence of the Church is God's sentence, according to Deut. 1:17: "You shall hear the little as well as the great: neither shall you respect any man's person, because it is the judgment of God." Therefore even those who are guilty of the prostitution of unbelief which is spiritual prostitution, should be received all the same.
Obj. 2: Further, Our Lord commanded Peter (Matt. 18:22) to forgive his offending brother "not" only "till seven times, but till seventy times seven times," which Jerome expounds as meaning that "a man should be forgiven, as often as he has sinned." Therefore he ought to be received by the Church as often as he has sinned by falling back into heresy.