2 And then expanding still further how it was that the Father should be glorified by the Son, He says: “As You have given Him power over all flesh, that He should give eternal life to all that You have given Him.” By all flesh, He meant every man, signifying the whole by a part; as, on the other hand, the whole man is signified by the superior part, when the apostle says, “Let every soul be subject to the higher powers.” For what else did He mean by “every soul,” save every man? And this, therefore, that power over all flesh was given to Christ by the Father, is to be understood in respect of His humanity; for in respect of His Godhead all things were made by Himself, and in Him were created all things in heaven and in earth, visible and invisible. “As,” then, He says, “You have given Him power over all flesh,” so may Your Son glorify You, in other words, make You known to all flesh whom You have given Him. For You have so given, “that He should give eternal life to all that You have given Him.”
3. “And this,” He adds, “is eternal life, that they may know You, the only true God, and Jesus Christ, whom You have sent.” The proper order of the words is, “That they may know You and Jesus Christ, whom You have sent, as the only true God.” Consequently, therefore, the Holy Spirit is also understood, because He is the Spirit of the Father and Son, as the substantial and consubstantial love of both. For the Father and Son are not two Gods, nor are the Father and Son and Holy Spirit three Gods; but the Trinity itself is the one only true God. And yet the Father is not the same as the Son, nor the Son the same as the Father, nor the Holy Spirit the same as the Father and the Son; for the Father and Son and Holy Spirit are three [persons], yet the Trinity itself is one God. If, then, the Son glorifies You in the same manner “as You have given Him power over all flesh,” and hast so given, “that He should give eternal life to all that You have given Him,” and “this is life eternal, that they may know You;” in this way, therefore, the Son glorifies You, that He makes You known to all whom You have given Him. Accordingly, if the knowledge of God is eternal life, we are making the greater advances to life, in proportion as we are enlarging our growth in such a knowledge. And we shall not die in the life eternal; for then, when there shall be no death, the knowledge of God shall be perfected. Then will be effected the full effulgence of God, because then the completed glory, as expressed in Greek by δόξα. For from it we have the word δόξασον, that is used here, and which some Latins have interpreted by “clarifica” (make effulgent), and some by “glorifica” (glorify). But by the ancients, glory, from which men are styled glorious, is thus defined: Glory is the widely-spread fame of any one accompanied with praise. But if a man is praised when the fame regarding him is believed, how will God be praised when He Himself shall be seen? Hence it is said in Scripture, “Blessed are they that dwell in Your house; they will be praising You for ever and ever.” There will God's praise continue without end, where there shall be the full knowledge of God; and because the full knowledge, therefore also the complete effulgence or glorification.
Source: Tractates on the Gospel of John (New Advent)