Ambrosiaster : By "secretly" he means that they had entered by deception, passing themselves off as brothers when they were enemies. By "slipped in" he means that they came in a humble manner, feigning friendship.… To "spy out" is to enter in such a way as to invent one thing and discover another, whereby they may challenge our liberty.… "Liberty in Jesus Christ" means not being subject to the law. "That they might bring us into bondage" means … to subject us to the law of circumcision. — EPISTLE TO THE Galatians 2.5.3-4 Hippolytus of Rome : "And they watched diligently." And this, too, is to be noted. For up to the present time both the Gentiles and the Jews of the circumcision watch and busy themselves with the dealings of the Church, desiring to suborn false witnesses against us, as the apostle says: "And that because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ Jesus." — Hippolytus Exegetical Fragments John Chrysostom : "And that because of the false brethren, privily brought in." Here arises a very important question, Who were these false brethren? If the Apostles permitted circumcision at Jerusalem, why are those who enjoined it, in accordance with the Apostolic sentence, to be called false brethren? First; because there is a difference between commanding an act to be done, and allowing it after it is done. He who enjoins an act, does it with zeal as necessary, and of primary importance; but he who, without himself commanding it, alloweth another to do it who wishes yields not from a sense of its being necessary but in order to subserve some purpose. We have a similar instance, in Paul's Epistle to the Corinthians, in his command to husbands and wives to come together again. To which, that he might not be thought to be legislating for them, he subjoins, "But this I say by way of permission, not of commandment." (1 Cor. vii: 5.) For this was not a judgment authoritatively given but an indulgence to their incontinence; as he says, "for your incontinency." Would you know Paul's sentence in this matter? hear his words, "I would that all men were even as I myself," (1 Cor. vii: 7.) in continence. And so here, the Apostles made this concession, not as vindicating the law, but as condescending to the infirmities of Judaism. Had they been vindicating the law, they would not have preached to the Jews in one way, and to the Gentiles in another. Had the observance been necessary for unbelievers, then indeed it would plainly have likewise been necessary for all the faithful. But by their decision not to harass the Gentiles on this point, they showed that they permitted it by way of condescension to the Jews. Whereas the purpose of the false brethren was to cast them out of grace, and reduce them under the yoke of slavery again. This is the first difference, and a very wide one. The second is, that the Apostles so acted in Judaea, where the Law was in force, but the false brethren, every where, for all the Galatians were influenced by them. Whence it appears that their intention was, not to build up, but entirely to pull down the Gospel, and that the thing was permitted by the Apostles on one ground and zealously practiced by the false brethren on another. "Who came in privily to spy out our liberty, which we have in Christ Jesus, that they might bring us into bondage." He points out their hostility by calling them spies; for the sole object of a spy is to obtain for himself facilities of devastation and destruction, by becoming acquainted with his adversary's position. And this is what those did, who wished to bring the disciples back to their old servitude. Hence too appears how very contrary their purpose was to that of the Apostles; the latter made concessions that they might gradually extricate them from their servitude, but the former plotted to subject them to one more severe. Therefore they looked round and observed accurately and made themselves busybodies to find out who were uncircumcised; as Paul says, "they came in privily to spy out our liberty," thus pointing out their machinations not only by the term "spies," but by this expression of a furtive entrance and creeping in. — Homily on Galatians 2 John Damascene : The preposition 'because of' (dia) was put here instead of 'according to' (kata). But the sense is this. The Apostles, he says, did not force Titus, who was uncircumcised, to be circumcised, although this was pointed out by the brethren who were brought in secretly and pressed for circumcision. Indeed he put them in the place of spies because of what is foreign to the truth. John Damascene : That they might introduce us again, he says, into the slavery of the law. This is why elsewhere he says, Christ purchased us from the curse of the law (Gal. 3:13). Oecumenius : Not because there were false brothers present, that is, pretend Christians, did the apostles compel Titus to be circumcised, which would have been a sign that Peter and his followers did not approve of circumcision. But there were certain false brothers in the appearance of brothers or Christians, preaching circumcision: not like Peter with the others out of accommodation and a certain allowance, but defending the matter as though it were a law. And the apostles tolerated this only with the Jews; those men even imposed circumcision among the Gentiles. For these were the Galatians who were causing disturbance. Nor, therefore, when they were present, he says, those whose work it was to preach circumcision, was Titus compelled to be circumcised. "who had secretly come in." He says the false brethren slipped in secretly, seeking to spy upon our freedom in Christ, that they might again subject us to the yoke of the law and to Judaic observances. For by not submitting to them he calls it freedom. See also how he showed them to be enemies, and entered as spoilers of the faith, first by saying, "who had secretly come in," indicating their secret and dangerous entrance, and by saying, "to spy." For he who spies does so with harm and deceit in mind. And, "in order to enslave us," he says. For indeed Peter and the other apostles allowed circumcision in order gradually to avoid the bondage of the law, whereas these imposed it so as to drive others into bondage. — Commentary on Galatians Tertullian : So great had been his desire to be approved and supported by those whom you wish on all occasions to be understood as in alliance with Judaism! When indeed he says, that "neither was Titus circumcised," he for the first time shows us that circumcision was the only question connected with the maintenance of the law, which had been as yet agitated by those whom he therefore calls "false brethren unawares brought in." These persons went no further than to insist on a continuance of the law, retaining unquestionably a sincere belief in the Creator. — Against Marcion Book V Tertullian : Therefore he says: "Because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ, that they might bring us into bondage, to whom we gave place by subjection not even for an hour." Let us only attend to the clear sense and to the reason of the thing, and the perversion of the Scripture will be apparent. — Against Marcion Book V Tertullian : "Liberty in Christ" has done no injury to innocence. — On Modesty