In John 17, we read the impressive prayer which the Son prays, just before He leaves to go to the Mount of Olives to be taken prisoner (John 18:1). He begins with …

These things speaks Jesus, and lifting His eyes to heaven, He said, “Father, come has the hour… John 17:1

And continues…

Now it is eonian life that they may know Thee (= Father), THE ONLY TRUE GOD, and Him Whom Thou dost commission, Jesus Christ. John 17:3

Here it is Jesus, Himself, Who calls His Father “the only true God”. He identifies Himself as the person Who is sent by “the only true God”. Theologians have tried to invalidated this unequivocal statement with an expressions found at the end of the first letter of John:

Yet we are aware that the Son of God is arriving, and has given us a comprehension, that we know the True One, and we are in the True One, in His Son, Jesus Christ. This One is the true God and life eonian. 1 John 5:20

They reason: the clause, “This One is the true God…”, belongs linguistically to the One just mentioned, and thus, Jesus Christ is the true God… . That would be in flagrant conflict with the previously quoted words of Jesus, Himself. Moreover, how can Jesus be “the true God”, if the preceding sentence calls Him the very Son of the True One? But then the reasoning itself, is it valid? Let’s apply it to, two earlier passages, where we also encounter the words, “this one is…” or “this is…”.

Who is the liar, if not he who is denying, saying that “Jesus is not the Christ”? This one is the antichrist, who is disowning the Father and the Son. 1John 2:22

If the words “this one is” must refer to what immediately preceded, then Jesus Christ, Himself, would be the antichrist! Another example:

… and every spirit which is not avowing Jesus the Lord having come in flesh is not of God. And this is that of the antichrist… 1 John 4:3

Here too, the context makes it clear that the words “this is…” do not refer to God, but to “every spirit which is not avowing Jesus.” With this in mind, let us go, once more, to 1John 5:20:

Yet we are aware that the Son of God is arriving, and has given us a comprehension, that we know the True One, and we are in the True One, in His Son, Jesus Christ. This One is the true God and life eonian.

It is absolutely clear that John, in his letters, is in perfect harmony with the words in his evangel-description (17:3). The only true God is He Whom we have gotten to know by His Son. And that also is the essence of eonian life.