Mark 9:40

But, inasmuch as they had prohibited the man from doing a thing in which, so far forth, he was really with them, the Lord said to them, "Forbid him not." For what they ought to have forbidden was what was outside their fellowship, so that they might bring him over to the unity of the Church, and not a thing like this, in which he was at one with them, that is to say, so far as he commended the name of their Master and Lord in the casting out of devils. And this is the principle on which the Catholic Church acts, not condemning common sacraments among heretics; for in these they are with us, and they are not against us. But she condemns and forbids division and separation, or any sentiment adverse to peace and truth. For therein they are against us, just because they are not with us in that, and because, not gathering with us, they are consequently scattering.

We must take care that this saying of the Lord appear not to be contrary to that, where He says, He who is not with me is against me. (Luke 11:23) Or will any one say that the difference lies in that here He says to His disciples, For he that is not against you is on your part, but in the other He speaks of Himself, He who is not with me is against me? As if indeed it were possiblel that he who is joined to Christ's disciples, who are as His members, should not be with Him. How if it were so, could it be true that he that receiveth you receiveth me? (Matt. 10:40) Or how is he not against Him, who is against His disciples? Where then will be that saying, He who despiseth you, despiseth me? But surely what is implied is, that a man is not with Him in as far as he is against Him, and is not against Him in as far as he is with Him. For instance, he who worked miracles in the name of Christ, and yet did not join himself to the body of His disciples, in as far as he worked the miracles in His name, was with them, and was not against them: again, in that he did not join their society, he was not with them, and was against them. But because they forbade his doing that in which he was with them, the Lord said unto them, Forbid him not; for they ought to have forbidden his being without their society, and thus to have persuaded him of the unity of the Church, but they should not have forbidden that in which he was with them, that is, his commendation of the name of their Lord and Master by the expulsion of devils. Thus the Church Catholic does not disapprove in heretics the sacraments, which are common, but she blames their division, or some opinion of theirs adverse to peace and to truth; for in this they are against us.

That both, therefore, should be true, as both are true,—both the declaration, that "he that is not with me is against me, and he that gathereth not with me scattereth abroad;" and also the injunction, "Forbid him not; for he that is not against you is for you,"—what must we understand, except that the man was to be confirmed in his veneration for that mighty Name, in respect of which he was not against the Church, but for it; and yet he was to be blamed for separating himself from the Church, whereby his gathering became a scattering; and if it should have so happened that he sought union with the Church, he should not have received what he already possessed, but be made to set right the points wherein he had gone astray?

What then does the Savior say? He did not allow John to forbid the one performing signs: "Do not forbid him," He says, "for no one who works a miracle in My name can soon afterward speak evil of Me." That is, how will the …

For how can he speak evil of Me, who draws glory from My name, and works miracles by the invocation of this very name. There follows, For he that is not against you is on your part.