Tractates on the Gospel of John

² But then after saying, “That they also may be one in us,” He added, “That the world may believe that You have sent me.” What does He mean by this? Is it that the world will then be brought to the faith, when we shall all be one in the Father and Son? Is not such a state the everlasting peace, and the reward of faith, rather than faith itself? For we shall be one not in order to our believing, but because we have believed. But although in this life, because of the common faith itself, all who believe in one are one according to the words of the apostle, “For you are all one in Christ Jesus;” even thus we are one, not in order to our believing, but because we do believe.

What, then, is meant by the words, “That they all may be one, that the world may believe”? This, doubtless, that the “all” are themselves the believing world. For those who shall be one are not of one class, and the world that is thereafter to believe in this very ground that these shall be one, of another; since it is perfectly certain that He says, “That they all may be one,” of those of whom He had said before, “Neither pray I for these alone, but for those also who shall believe in me through their word,” immediately adding as He does, “That they all may be one.”

And this “all,” what is it but the world; not certainly that which is hostile, but that which is believing? For you see here that He who had said, “I pray not for the world,” now prays for the world that it may believe. For there is a world whereof it is written, “That we might not be condemned with this world.” For that world He prays not, for He is fully aware to what it is predestinated. And there is a world whereof it is written, “For the Son of man came not to condemn the world, but that the world through Him might be saved;” and hence the apostle also says, “God was in Christ, reconciling the world unto Himself.” For this world it is that He prays, in saying, “That the world may believe that You have sent me.”

For through this faith the world is reconciled unto God when it believes in the Christ whom God has sent. How, then, are we to understand Him when He says, “That they also may be one in us, that the world may believe that You have sent me,” but just in this way, that He did not assign the cause of the world believing to the fact that those others are one, as if it believed on the ground that it saw them to be one; for the world itself here consists of all who by their own believing become one; but in His prayer He said, “That the world may believe,” just as in His prayer He also said, “That they all may be one;” and still further in the same prayer, “That they also may be one in us.”

For the words, “they all may be one,” are equivalent to “the world may believe,” since it is by believing that they become one, perfectly one; that is, those who, although one by nature, had ceased to be so by their mutual dissensions. In fine, if the verb which He uses, “I pray,” be understood in the third clause, or rather, to make the whole fuller, be everywhere supplied, the explanation of this sentence will be all the clearer: I pray “that they all may be one; as Thou, Father, in me, and I in You;” I pray “that they also may be one in us;” I pray “that the world may believe that You have sent me.”

And, mark, He added the words “in us” in order that we may know that our being made one in that love of unchanging faithfulness is to be attributed to the grace of God, and not to ourselves: just as the apostle, after saying, “For you were at one time darkness, but now are you light,” that none might attribute the doing of this to themselves, added, “in the Lord.”