2264 Note that when he prayed for their sanctification he called the Father holy Father (v 11). But now, calling for retribution, he refers to the Father as righteous Father. This eliminates the old error which said that there was a just God, the God of the Old Testament, and another God who was good, the God of the New Testament.
The failure of the world concerned its knowledge of God. He says, the world, not as reconciled, but damned, has not known you: "The world was made through him, yet the world knew him not" (1:10).
2265 But this seems to conflict with Romans (1:19) "For what can be known about God is plain to them. Ever since the creation of the world his invisible nature, namely, his eternal power and deity, has been clearly perceived in the things that have been made." We should say to this that knowledge is of two kinds: one is speculative, and the other affective. Through neither of these ways did the world know God completely. Although some Gentiles knew God as having some of those attributes which are knowable by reason, they did not know God as the Father of an only begotten and consubstantial Son ‑ and our Lord is talking about knowledge of these things.
Again, if they did have some speculative knowledge of God, this was mixed with many errors: some denied his providence over all things; others said he was the soul of the world; still others worshipped other gods along with him. For this reason they are said not to know God. Composite things can be known in part, and unknown in part, while simple things are unknown if they are not known in their entirety. Thus, even though some erred only slightly in their knowledge of God, they are said to be entirely ignorant of him. Consequently, since these people did not know the special excellence of God, they are said not to know him: "For although they knew God they did not honor him as God or give thanks to him, but they became futile in their thinking and their senseless minds were darkened" (Rom 1:21); "Nor did they recognize the craftsman while paying heed to his works" (Wis 13:1).
Furthermore, the world did not know God by an affective knowledge, because it did not love him, "like heathen who do not know God" (1 Thess 4:5). So he says, the world has not known you, that is, without error, and as a Father, through love. [35]
2266 Then the progress of the disciples is mentioned (v 25b). First, their progress in knowledge; secondly, the fruit of this knowledge (v 26). As regards the disciples' progress in knowledge he does three things: first, he gives the root and fountain of this knowledge of God; secondly, the rivulets and streams that flow from it; thirdly, we see their origin in the root or fountain.
2267 The root and fountain of our knowledge of God is the Word of God, that is, Christ: "The fountain of wisdom is the word of God" [Sir 1:5]. Human wisdom consists in knowing God. But this knowledge flows to us from the Word, because to the extent that we share in the Word of God, to that extent do we know God. Thus he says, the world has not known you in this way, but I , the fountain of wisdom, your Word, have known you, eternally and fully: "If I said, I do not know him, I should be a liar like you" (8:55).
2268 From this knowledge of the Word, which is the root and fountain, flows, like rivulets and streams, all the knowledge of the faithful. Accordingly he says, and these know that [ quia , meaning "that," or "because"] you have sent me . Augustine understands the word as meaning "because," and it then indicates the reason for their knowledge. [36] The meaning is then: I have known you, by nature, and these know you by grace. Why? Because you have sent me, so that they may know you: "For this was I born, and for this I have come into the world, to bear witness to the truth" (18:37); "I have manifested your name" (17:6).
If we understand the word as meaning "that," it then refers to what is known. The meaning is: and these know. What do they know? That you have sent me, because he who sees the Son also sees the Father (14:9).
2269 They did not know this by themselves; they learned it from me because "No one knows the Father except the Son and any one to whom the Son chooses to reveal him" (Mt 11:27). So he says, I made known to them your name, and I will make it known. He is indicating the two types of knowledge which the faithful have through him. First, there is the knowledge of his teaching, and he refers to this by saying, I made known to them your name, teaching them by my external words: "No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known" (1:18); "It was declared at first by the Lord, and it was attested to us by those who heard him" (Heb 2:3).
The other knowledge is from within, through the Holy Spirit. Referring to this he says, and I will make it known by giving them the Holy Spirit: "When the Spirit of truth comes, he will teach you all truth" [16:13].
Or, alternatively, I made known to them your name by the knowledge of faith, "for now we see in a mirror dimly," and I will make it known through the vision of glory in their homeland, where they will see "face to face" (1 Cor 13:12).
2270 The fruit of this knowledge is that the love with which you have loved me may be in them, and I in them. This can be explained in two ways. The first and better way is that since the Father loves the Son, as is shown by the glory he gave him, consequently, he loves all those in whom the Son is present ‑ and the Son is in them insofar as they have knowledge of the truth. So the meaning is this: I will make your name known to them; and by the fact that they know you, I, your Word, will be in them; and by the fact that I am in them, the love with which you love me may be in them, that is, will be given to them, and you will love them as you have loved me.
Here is the other explanation: that the love with which you have loved me may be in them, that is, as you have loved me, so they, by sharing in the Holy Spirit, may love. And by that fact I will be in them as God in a temple, and they in me, as members of the head: "He who abides in love abides in God, and God abides in him" (1 Jn 4:16).
[1] St. Thomas refers to Jn 17:1 in the Summa Theologiae: III, q. 21, a. 3, s. c.; q. 83, a. 4, ad 2; Jn 17:3: ST I, q. 18, a. 2, obj. 3; q. 31, a. 4, obj 1; I-II, q. 3, a. 2, ad 1; q. 3, a. 4, s. c.; q. 114, a. 4, s. c.; II-II, q. 1, a. 8; q. 24, a. 12, s. c.; III, q. 9, a. 2, obj. 2; q. 59, a. 5, ad 1; Jn 16:5: ST I, q. 46, a. 1, s. c.; Jn 17:5: ST III, q. 83, a. 4, ad 7.
[2] De Trin ., 9, ch. 31; PL 10; cf. Catena Aurea, 17:1-5.
[3] De Trin ., 5, ch. 3; PL 10; cf. Catena Aurea, 17:1-5.
[4] De Trin ., 3, ch. 14; PL 10; cf. Catena Aurea, 17:1-5.
[5] Augustine, De Trin ., 6, ch. 9; cf. Catena Aurea , 17:1-5.
[6] Augustine, De Trin ., 105, ch. 5; cf. Catena Aurea , 17:1-5.
[7] Summa-Christ's human nature is glorified, but remains human.
[8] Hilary, De Trin ., 3; PL 10; cf. Catena Aurea, 17:1-5.
[9] St. Thomas refers to Jn 17:6 in the Summa Theologiae: II-II, q. 2, a. 8, obj. 2; Jn 17:10: ST III, q. 48, a. 1, s. c.
[10] Tract. in Io ., 106, ch. 1, col. 1908; cf. Catena Aurea , 17:6-8.
[11] In Ioannem hom ., 81, ch. 1; PG 59, col. 437; cf. Catena Aurea , 17:6-8.