And this is life eternal, that they might know thee the {b} only true God, and Jesus Christ, whom thou hast sent.

(b) He calls the Father the only true God in order to set him against all false gods, and to include himself and the Holy Spirit, for he immediately joins the knowledge of the Father and the knowledge of himself together, and according to his accustomed manner sets forth the whole Godhead in the person of the Father. So is the Father alone said to be King, immortal, wise, dwelling in light which no man can attain unto, and invisible; Ro 16:27; 1Ti 1:17.

People's New Testament

17:3 This life is eternal, that they might know thee, etc. The knowledge of God as manifested in Jesus Christ is the first requisite to salvation and life eternal. They key to that knowledge is faith and love.

Wesley's Notes

17:3 To know - By loving, holy faith, thee the only true God - The only cause and end of all things; not excluding the Son and the Holy Ghost, no more than the Father is excluded from being Lord, 1Cor 8:6; but the false gods of the heathens; and Jesus Christ - As their prophet, priest, and king: this is life eternal - It is both the way to, and the essence of, everlasting happiness.

Jamieson-Fausset-Brown Bible Commentary

3. this is-that.

life eternal, that they might-may.

know, &c.-This life eternal, then, is not mere conscious and unending existence, but a life of acquaintance with God in Christ (Job 22:21).

thee, the only true God-the sole personal living God; in glorious contrast equally with heathen polytheism, philosophic naturalism, and mystic pantheism.

and Jesus Christ whom thou hast sent-This is the only place where our Lord gives Himself this compound name, afterwards so current in apostolic preaching and writing. Here the terms are used in their strict signification-"Jesus," because He "saves His people from their sins"; "Christ," as anointed with the measureless fulness of the Holy Ghost for the exercise of His saving offices (see on [1874]Mt 1:16); "Whom Thou hast sent," in the plenitude of Divine Authority and Power, to save. "The very juxtaposition here of Jesus Christ with the Father is a proof, by implication, of our Lord's Godhead. The knowledge of God and a creature could not be eternal life, and such an association of the one with the other would be inconceivable" [Alford].

Matthew Henry's Concise Commentary

17:1-5 Our Lord prayed as a man, and as the Mediator of his people; yet he spoke with majesty and authority, as one with and equal to the Father. Eternal life could not be given to believers, unless Christ, their Surety, both glorified the Father, and was glorified of him. This is the sinner's way to eternal life, and when this knowledge shall be made perfect, holiness and happiness will be fully enjoyed. The holiness and happiness of the redeemed, are especially that glory of Christ, and of his Father, which was the joy set before him, for which he endured the cross and despised the shame; this glory was the end of the sorrow of his soul, and in obtaining it he was fully satisfied. Thus we are taught that our glorifying God is needed as an evidence of our interest in Christ, through whom eternal life is God's free gift.