e 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."
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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