My top 10 biblical and exegetical reasons Jesus Christ is the True God and Eternal Life.
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- Jesus is also the True God and the True one in 1 John. Jesus is the true light which brings light to all men (
John 1:9) Jesus is the truth (
John 14:6)Jesus is the true vine (
John 15:1). Jesus is the true witness of God (
John 18:37) He who is true (
Revelation 3:7) Jesus is the faithful and true witness (
Revelation 3:14)Jesus is Lord God Almighty, Just and true are your ways(
Revelation 15:3) Jesus is faithful and true(
Revelation 19:11).
8th-
[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.
9th- Netbible- Wallace
If This one in 5:20 is understood as referring to Jesus, it forms an inclusion with the prologue, which introduced the reader to "the eternal life which was with the Father and was manifested to us." Thus it appears best to understand the pronoun This one in 5:20 as a reference to Jesus Christ. The christological affirmation which results is striking, but certainly not beyond the capabilities of the author (see
John 1:1 and 20:28):
This One [Jesus Christ] is the true God and eternal life.
10th- This/ He (autos)Jesus Christ (the last-named Person) is the true God
Conclusion: 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 NT 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 makes absolutely no sense whatsoever unless John is identifying Jesus as the true God and refuting the Gnostics of his day who denied the Incarnation.This is the last of the contrasts of which the Epistle is so full. We have had light and darkness, truth and falsehood, love and hate, God and the world, Christ and Antichrist, life and death, doing righteousness and doing sin, the children of God and the children of the devil, the spirit of truth and the spirit of error, the believer untouched by the evil one and the world lying in the evil one; and now at the close we have what in that age was the ever present and pressing contrast between the true God Jesus Christ and the idols.
hope this helps !!!