1 John 2:25

‘And this is the promise which he promised us, even the life eternal.'

It is worth making sure that they do so, for ‘He' has promised eternal life to those who truly know Him. Eternal life consists in knowing the only true God and Jesus Christ Whom He had sent (John 17:3). It is therefore bound up in both the only true God and in Jesus Christ as the ambassador of the only true God. This does not necessarily separate the only true God and Jesus Christ. Just as an ambassador may be sent by a government of which he is a part, as its representative, so that he is both an essential part of the government and its representative, so Jesus was sent by the only true God, the Godhead of which He is a part, as the representative of the Godhead. (Compare 1 John 5:20)

But Who is it Who has promised us eternal life? The nearest antecedent is the Father. But the emphasis in the context is on the Son. The ambiguity may be deliberate. In John 5:24 eternal life was God's gift to those who heard Jesus' words, which includes responding to them, which meant those who believed Him that sent Him. Thus they were to respond to both the Son and the Father. Such people passed immediately from death to life, and were guaranteed their part in the resurrection (John 5:29). Indeed Jesus Himself gives eternal life to those who hear His voice and follow Him. They are thus revealed as known by Him and given to Him by the Father (John 10:28). So the source of eternal life is both Father and Son. And that eternal life is a present reality. As John tells us in 1 John 5:13, we may know that we  have  (not ‘will have) eternal life.

Eternal life is a theme of the letter. It came in the One Who was heard, seen and handled, the Word of life (1 John 1:1), and consisted of coming to know God as light and entering into fellowship with Him (1 John 1:5), and being right with Him (1 John 2:1) through Jesus Christ. No one who hates his brother has eternal life (1 John 3:15) because he thereby reveals that he is in darkness, rejects the true witness to God, and is without the anointing (1 John 2:9; 1 John 2:19) It is given by the Father, and is bound up in His Son (1 John 5:11) so that he who has the Son has life, while he who does not have the Son does not have life (1 John 5:12). It is also given by the Son (John 10:28). It consists of a true spiritual knowledge of God in Christ and in our abiding in Him, enjoying His life within us.

Thus by believing fully in the Son of God we can know that we have eternal life. It is finally defined in 1 John 5:20, which expands on John 17:3, as ‘we know that the Son of God is come, and has given us an understanding, that we may know Him Who is true, and we are in Him Who is true, even in his Son Jesus Christ. This is the true God, and eternal life.' This is basically declaring that it comes through knowing that the Son of God has come, receiving understanding from Him, thus knowing and being in full relationship with Him Who is true (the Father), by which we are in Him and His Son Jesus Christ, Who are together the true God and bestowers of eternal life.

Elsewhere eternal life is a gift men seek (Mark 10:17; Luke 10:25; Luke 18:18; John 5:39) and is for those who follow Him (Mark 10:30). It is the opposite of perishing (John 3:15), and comes through participation in His sacrifice of Himself (John 6:54). In Paul, who looks to the grand consummation and complete fulfilment of it, it is always future (Romans 2:7; Romans 5:21; Rom 6:3; 1 Timothy 6:12; 1 Timothy 6:19; Titus 1:2; Titus 3:7). But John sees the present experience as well as the future glory.