5:20 And we know that the Son of God has come and has given us insight to know him who is true, and we are in him who is true, in his Son Jesus Christ. This one is the true God and eternal life.

Is John referring to the Father or to the Son as ‘the true God’?

(a) Some commentators understand John to mean that ‘the true God’ refers to the Father (so Westcott, Dodd, Grayston, Smalley, Stott).  The idea that the Father is ‘the true God’ and the source of eternal life is uncontroversial, and supported by Jn 17:3; 1 Thess 1:9 etc).

Akin (while, on balance, not supporting this interpretation) notes the following points in favour:

(i) The word houtos does not necessarily refer to the closest antecedent (cf. 2:22; 2 John 7) and therefore can refer back to God the Father.

(ii) It is John’s style to repeat what has already been stated and then add to it.

(iii) The Father can more properly be described as the source of life (John 5:26).

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(b) Others think that it is God’s Son, Jesus Christ, who is being referred as ‘the true God’ (so Luther and Calvin, and more recently Akin, Barker, Brown, Bruce, Bultmann, Haas, Johnson, Marshall, Plummer, and Schnackenburg).  Although this would then be a most direct and striking assertion of our Lord’s deity, it does have precedent in Jn 1:1.

Akin lists the following reasons for adopting this interpretation:

(i) “Jesus Christ” is the nearest antecedent to the pronoun.

(ii) It would be repetitive to state that God is “true” after having already stated that “who are in him who is true” earlier in the verse.

(iii) Jesus was designated as the source of eternal life in 1 jn 1:2 (cf. 5:12; John 11:25; 14:6).

(iv) First John 5:6 begins in the same way as this phrase (houtos estin), and there it clearly refers to Jesus Christ.

(v) John has referred to Jesus as “God” on other occasions (John 1:1, 18; 20:28). Marshall rightly comments, “It is fitting that at the climax of the Epistle, as at the beginning and climax of the Gospel of John (Jn. 1:1; 20:28), full deity should be ascribed to Jesus.”

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Marshall (IVPNTC) says much the same thing:

‘Although good sense can be made of either reading, a reference to Jesus Christ is supported by the following facts: First, in both the Gospel and epistle, although it is said that God gives eternal life, “life” as a predicate always refers to Jesus Christ; (Jn 11:25; 14:6; 1 Jn 1:2) second, the Gospel calls the Word “God,” (Jn 1:1,18) as it also does the Risen Christ (Jn 20:28). Third, the nearest antecedent of the Greek demonstrative pronoun “this” is “Jesus Christ.”‘

As Johnson observes:

‘Elsewhere the Johannine writings call Jesus “God” (John 1:1, 18; 20:28) and treat him as equal with God (e.g., John 5:18; 8:58; 10:30; 14:7–9; 17:11, 22–23).’

The same writer adds:

‘It is more likely that the Elder would end his exhortation with a resounding affirmation of the full deity of the human Jesus, the key truth denied by the secessionist false teachers, and with the assertion, against them, that to know this Jesus is to have eternal life itself (cf. 5:11–13).’

Kruse cites Schnackenburg:

‘Here the full identity of Jesus with God is recognized without reserve (note the article with theos, God). This seems to occur intentionally at the end of the letter, at the climax of the triumphant expression of faith. It is hardly an accident that it is precisely at the beginning (1:1, 18) and the end (20:28) of the Gospel of John that the light of Jesus’ divinity shines forth most fully. The climactic christological confession becomes visible here in all its clarity.’

Jobes writes that, in any case, all that John says about the Father is true of the Son:

‘Even if “Christ” is not the explicit antecedent, John’s logic requires this to be a statement of Jesus’ deity, and all that Dodd sees gathered together is gathered in Jesus Christ. For by John’s statement, to be “in the True One” means to be “in Jesus Christ.” It is only by being in the True God who is eternal life that anyone can have eternal life.’

We would add that, if John’s Gospel has an inclusio that emphasises Christ’s deity, then so does his 1st Epistle, for the reference to our Lord as ‘the eternal life’ (1 Jn 1:2) is matched (according to this second, and preferable, interpretation) by precisely the same designation here in 5:20.