The Son of God is the Son of the Father.
2 John 1
3Grace, mercy and peace from
God the Father and from Jesus Christ, the Father’s Son, will be with us in truth and love.
In all Scriptural precedent, the true God is the Father: Jeremiah 10:10, John 17:3, 1 Thess. 1:9,10
In all Scriptural precedent, the only God is the Father: Malachi 2:10, John 17:3, Ephesians 4:6, 1 Corinthians 8:6
Therefore, in 1 John 5:20, when it refers to "the true God" it refers to the only God mentioned in the verse, which would be the God Jesus is the Son of, the Father. The Father is the True God. It's a Unitarian verse.
Jesus is eternal life, He is life. We see this over and over again in the Apostle Johns writings. In Him was LIFE and that LIFE was the light of man. Life of the world, the Bread of LIFE,My words are spirit and they are LIFE, I AM the way,the truth and the LIFE,The LIFE was manifested and we proclaim to you the ETERNAL Life which was with the Father, and was manifested to us- The Prologue of 1st John. So we see that when John uses the phrase True God and Eternal Life together in 1 John 5:20 that He is referring to Christ as the closest antecedent making Him the True God and Eternal Life.
Also we see that when we search the GNT that Eternal Life is never used of the Father without the Son but we see that Eternal Life is used over and over with Jesus where the Father is never mentioned. This makes a solid case for Jesus in 1 John 5:20 as the True God and Eternal Life.
1 John 5:20
20 We know also that the Son of God has come and has given us understanding, so that we may know him who is true. And we are in him who is true — even in his Son Jesus Christ. He(Jesus) is the true God and eternal life.
On behalf of seeing
χριστος as the antecedent are the following arguments: (1) Although it is true that
αληθινος θεος is not elsewhere referred to Christ,
αληθεια is, and is so in Johannine literature (John 14:6).
29 Winer-Moulton, 195.
Further,
αληθινος θεος is not a "constant.. epithet" as Winer supposes, being found only in John 17:3 and 1 John 5:20! (2)
Christ is also said to be ζωη in John's writings John 11:25; 14:6; 1 John 1:1-2), an epithet nowhere else used of the Father. (3) The demonstrative pronoun,
ουτος, in the Gospel and Epistles of John seems to be used in a theologically rich manner.30 Specifically,
of the approximately seventy instances in which ουτος has a personal referent, as many as forty- four of them (almost two-thirds of the instances) refer to the Son. Of the remainder, most imply some sort of positive connection with the Son.31 What is most significant is that never is the Father the referent.For what it is worth, this datum increases the probability that
ιησου χριστω is the antecedent in 1 John 5:20. 32 The issue cannot be decided on grammar alone. But suffice it to say here that
there are no grammatical reasons for denying that αληθινος θεος is descriptive of Jesus Christ.
1st- Jesus is called God in the writings of John(1:1,20:28,1 John 5:20)
2nd- Jesus is called Eternal Life over and over again in Johns writings
3rd- John opens up his epistle with the Eternal life(Jesus) that was with the Father in the beginning and was manifest to the disciples(1 John 1:1-5)
4th- John ends his epistle with Jesus who is eternal life and only is eternal life found in Him who is the true God.
5th- never is eternal life used of the Father alone. When the Father is included the Son is always mentioned together with the Father making them equal. Equality with the Father was not something Jesus needed to grasp at as He already possessed complete Deity as God.(Phil 2, Col 2:9)
6th- John would not leave his readers with any ambiguity warning them to guard themselves from idols(5:21) So this would be clear his reference was to those who reject Jesus as the true God. They are the idoloters and antichrists John writes of in his epistles.
7th-
[In John's writings] Of the approximately
70 instances in which
ουτος has a personal referent, as many as
44 of them (almost
2/3 . . . ) refer to the Son. Of the remainder, most imply some sort of positive connection with the Son.31
What is most significant is that NEVER is the Father the referent.FWIW, this datum increases the probability that
ιησου χριστω IS the antecedent in 1 John 5:20. Wallace.
So the most logical conclusion is that it refers to Jesus as the true God. Not only is this Wallace's conclusion from Johns usage of outos but He is the closest antecedent (most times in the GNT this principal holds true). Eternal Life is never used of the Father alone in John’s writings and only a couple of times does John include the Father with the Son regarding eternal life. John opens up his epistles describing the "eternal life" who was with the Father in the beginning and then ends his epistle with eternal life identifying Jesus as the true God and eternal life. John then says this in the last verse:
1 John 5:21-Guard yourselves from idols
Now why would he leave any ambiguity in verse 20 as to the identity of the true God and eternal life then turn around commanding them to protect themselves from idolatry ? It make absolutely no sense whatsoever unless John is identifying Jesus as the true God and refuting the Gnostics of his day who denied the Incarnation.
More evidence from Scripture that Jesus is life, the source of that life and eternal life itself. Apart from Him there is no life. This cannot be said of a mere man now can it ?
John 1:4
4
In Him was life, and
the life was the Light of men.
John 5:39-40
39 You diligently study the Scriptures because you think that by them you possess eternal life. These are the Scriptures that testify about Me, 40 yet you refuse to come
to Me to have life.
John 6:33
For the bread of God is He which cometh down from heaven, and
giveth life unto the world.
John 6:35
35 And Jesus said unto them
, I Am the bread of life:
John 6:47
47 Verily, verily, I say unto you, He that believeth on
Me hath everlasting life.
John 6:51
51 I Am the living bread which came down from heaven: if any man eat of this bread, he
shall live for ever: and the bread that I will give is my flesh, which
I will give for the life of the world.
John 6:53
53 Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have
no life in you.
John 6:63
63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and
they are life.
John 10:10
10 The thief comes only to steal and kill and destroy; I have come that they may have
life, and have it to the full.
John 11:25-26
25 Jesus said to her, "I Am the resurrection and
the life; he who believes in Me will live even if he dies, 26 and everyone who lives and
believes in Me will never die. Do you believe this?"
John 14:6
6 Jesus said to him,
"I Am the way, and the truth, and
the life; no one comes to the Father but through Me.
John 20:30-31
30 Therefore many other signs Jesus also performed in the presence of the disciples, which are not written in this book; 31 but these have been written so that you may believe that Jesus is the Christ, the Son of God; and that believing you may
have life in His name.
1 John 1:1-2
1 What was from the beginning, what we have heard, what we have seen with our eyes, what we have looked at and touched with our hands, concerning
the Word of Life — 2 and
the life was manifested, and we have seen and testify and proclaim to you the
eternal life, which was with the Father and was manifested to us
1 John 5:12-13
12 He who has the Son has
the life; he who does not have the Son of God does not have the life. 13 These things I have written to you who
believe in the name of the Son of God, so that you may know that you
have eternal life.
1 John 5:20
20 We know also that the Son of God has come and has given us understanding, so that we may know him who is true. And we are in Him who is true — even in His Son
Jesus Christ. He is the true God and eternal life
And Jesus said no one knows the Father but through the Son. They are One in nature,essence or being. You cannot have One without the Other. This can be said of no man unless that man is also God in the flesh which Jesus is indeed !
hope this helps !!!