John 10:16

Observe again, the word "must," here used, doth not express necessity, but is declaratory of something which will certainly come to pass. As though He had said, "Why marvel ye if these shall follow Me, and if My sheep shall hear My voice? When ye shall see others also following Me and hearing My voice, then shall ye be astonished more." And be not confounded when you hear Him say, "which are not of this fold", for the difference relateth to the Law only, as also Paul saith, "Neither circumcision availeth anything, nor uncircumcision." "Them also must I bring." He showeth that both these and those were scattered and mixed, and without shepherds, because the good Shepherd had not yet come. Then He proclaimeth beforehand their future union, that, "They shall be one fold." Which same thing also Paul declared, saying, "For to make in Himself of twain one new man." (Eph. ii. 15.)

(de Verb. Dom. s. 1) The sheep hitherto spoken of are those of the stock of Israel according to the flesh. But there were others of the stock of Israel, according to faith, Gentiles, who were as yet out of the fold; predestinated, but not yet gathered together. They are not of this fold, because they are not of the race of Israel, but they will be of this fold: Them also I must bring. (Tr. xlvii. 4) What does He mean then when He says, I am not sent but unto the lost sheep of the house of Israel? Only, that whereas He manifested Himself personally to the Jews, He did not go Himself to the Gentiles, but sent others.

But of the one sheepfold and of the one Shepherd, you are now indeed being constantly reminded; for we have commended much the one sheepfold, preaching unity, that all the sheep should enter by Christ, and none of them should follow Donatus. Nevertheless, for what particular reason this was said by the Lord, is sufficiently apparent. For He was speaking among the Jews, and had been specially sent to the Jews, not for the sake of that class who were bound up in their inhuman hatred and persistently abiding in darkness, but for the sake of some in the nation whom He calls His sheep: of whom He saith, "I am not sent but to the lost sheep of the house of Israel." But perhaps some one thinks that, as He Himself came not to us, but sent, we have not heard His own voice, but only the voice of those whom He sent. Far from it: let such a thought be banished from your hearts; for He Himself was in those whom He sent. Listen to Paul himself whom He sent; for Paul was specially sent as an apostle to the Gentiles; and it is Paul who, terrifying them not with himself but with Him saith, "Do ye wish to receive a proof of Him who speaketh in me, that is, of Christ?" Listen also to the Lord Himself. "And other sheep I have," that is, among the Gentiles, "which are not of this fold," that is, of the people of Israel: "them also must I bring." Therefore, even when it is by the instrumentality of His servants, it is He and not another that bringeth them. Listen further: "They shall hear my voice." See here also, it is He Himself who speaks by His servants, and it is His voice that is heard in those whom He sends. "That there may be one fold, and one shepherd." Of these two flocks, as of two walls, is the corner-stone formed. And thus is He both door and the corner-stone: all by way of comparison, none of them literally.

(Hom. xiv.) But as He came to redeem not only the Jews, but the Gentiles, He adds, And other sheep I have, which are not of this fold. (Hom. Evang. xiv.) Of two flocks He maketh one fold, uniting the Jews and Gentiles in His faith.

For there is one sign of baptism for all, and one Shepherd, even the Word of God. Let the Manichean mark; there is but one fold and one Shepherd set forth both in the Old and New Testaments.