Reply Obj. 2: Those Jews who have in no way received the faith, ought not by no means to be compelled to the faith: if, however, they have received it, they ought to be compelled to keep it, as is stated in the same chapter.
Reply Obj. 3: Just as taking a vow is a matter of will, and keeping a vow, a matter of obligation, so acceptance of the faith is a matter of the will, whereas keeping the faith, when once one has received it, is a matter of obligation. Wherefore heretics should be compelled to keep the faith. Thus Augustine says to the Count Boniface (Ep. clxxxv): "What do these people mean by crying out continually: 'We may believe or not believe just as we choose. Whom did Christ compel?' They should remember that Christ at first compelled Paul and afterwards taught Him."
Reply Obj. 4: As Augustine says in the same letter, "none of us wishes any heretic to perish. But the house of David did not deserve to have peace, unless his son Absalom had been killed in the war which he had raised against his father. Thus if the Catholic Church gathers together some of the perdition of others, she heals the sorrow of her maternal heart by the delivery of so many nations." _______________________
NINTH ARTICLE [II-II, Q. 10, Art. 9]
Whether It Is Lawful to Communicate with Unbelievers?
Objection 1: It would seem that it is lawful to communicate with unbelievers. For the Apostle says (1 Cor. 10:27): "If any of them that believe not, invite you, and you be willing to go, eat of anything that is set before you." And Chrysostom says (Hom. xxv super Epist. ad Heb.): "If you wish to go to dine with pagans, we permit it without any reservation." Now to sit at table with anyone is to communicate with him. Therefore it is lawful to communicate with unbelievers.
Obj. 2: Further, the Apostle says (1 Cor. 5:12): "What have I to do to judge them that are without?" Now unbelievers are without. When, therefore, the Church forbids the faithful to communicate with certain people, it seems that they ought not to be forbidden to communicate with unbelievers.
Obj. 3: Further, a master cannot employ his servant, unless he communicate with him, at least by word, since the master moves his servant by command. Now Christians can have unbelievers, either Jews, or pagans, or Saracens, for servants. Therefore they can lawfully communicate with them.
On the contrary, It is written (Deut. 7:2, 3): "Thou shalt make no league with them, nor show mercy to them; neither shalt thou make marriages with them": and a gloss on Lev. 15:19, "The woman who at the return of the month," etc. says: "It is so necessary to shun idolatry, that we should not come in touch with idolaters or their disciples, nor have any dealings with them."
I answer that, Communication with a particular person is forbidden to the faithful, in two ways: first, as a punishment of the person with whom they are forbidden to communicate; secondly, for the safety of those who are forbidden to communicate with others. Both motives can be gathered from the Apostle's words (1 Cor. 5:6). For after he had pronounced sentence of excommunication, he adds as his reason: "Know you not that a little leaven corrupts the whole lump?" and afterwards he adds the reason on the part of the punishment inflicted by the sentence of the Church when he says (1 Cor. 5:12): "Do not you judge them that are within?"