Albert Barnes Commentary John 17:3

"And this is life eternal, that they should know thee the only true God, and him whom thou didst send, [even] Jesus Christ." — John 17:3 (ASV)

This is life eternal. This is the source of eternal life, or it is in this manner that it is to be obtained. The knowledge of God and of His Son Jesus Christ is itself a source of unspeakable and eternal joy. (John 6:63; John 12:50).

Might know thee. The word know here, as in other places, expresses more than a mere speculative acquaintance with the character and perfections of God. It includes all the impressions on the mind and life which a just view of God and of the Savior is fitted to produce. It includes, of course, love, reverence, obedience, honor, gratitude, and supreme affection. To know God as He is, is to know and regard Him as a lawgiver, a sovereign, a parent, and a friend. It is to yield the whole soul to Him and strive to obey His law.

The only true God. The only God, in opposition to all false gods. What is said here is in opposition to idols, not to Jesus Himself, who, in 1 John 5:20, is called the true God and eternal life.

And Jesus Christ. To know Jesus Christ is to have a practical impression of Him as He is; that is, to allow His character and work to make their due impression on the heart and life. Simply to have heard that there is a Savior is not to know it. To have been taught in childhood and trained up in the belief of it is not to know it. To know Him is to have a just, practical view of Him in all His perfections—as God and man; as a mediator; as a prophet, a priest, and a king. It is to feel our need of such a Savior, to see that we are sinners, and to yield the whole soul to Him, knowing that He is a Savior fitted to our wants, and that in His hands our souls are safe. (Titus 1:16; Philippians 3:10; 1 John 5:20).

In this verse is contained the sum and essence of the Christian religion, as it is distinguished from all the schemes of idolatry and philosophy, and all the false plans on which people have sought to obtain eternal life.

The Gentiles worshipped many gods; the Christian worships one—the living and the true God. In contrast, the Jew, the Deist, the Muslim, and the Socinian profess to acknowledge one God, but they do so without any atoning sacrifice and Mediator.

The true Christian, however, approaches Him through the great Mediator, equal with the Father, who for us became incarnate and died that He might reconcile us to God.