John makes it clear once again that what he wrote in John 1:1–2 is very important. He proclaims what he and the other ear and eye witnesses of Jesus Christ have seen and heard. That is what the readers and hearers of this letter really need to know. It is not merely an opinion; it is the truth. This is factual. It is the Lord Jesus who also commissioned the apostles to proclaim these facts throughout the world. We read this, among other places, in Matthew 28:19–20, Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you.
It is precisely this testimony of the ear and eye witness, being proclaimed by the apostles, that causes us to belong to the apostles, and that we also want to carry that very testimony out into the world again and again.
John makes it clear that we only truly belong to the apostles when we believe exactly what they told us. Here John also points to the people who have left the church—those who say they believe in Jesus differently; those who at least want the freedom to do so; those who are even trying to get the churches to whom John is writing into their camp. From the sequel to this verse, it becomes clear that these churches, these believers, have to choose between the testimony of the ear and eye witnesses and the people who believe in Jesus in their own way. This includes the fact that Jesus is proclaimed as not being the Son of God. The Son of God could never have become truly human, nor would this even be necessary to redeem us from the penalty of our sins and guilt.
John makes it clear how decisive the fellowship with the ear and eye witnesses is. You can also find here an important purpose of writing this letter. John’s overall goal is that the people to whom he is writing are truly connected and remain connected to Christ. It is that connection, that fellowship, which is at stake here.
The Holy Spirit makes it clear through John that being connected to the testimony of the ear and eye witnesses of Christ’s ministry is decisive as to whether one is truly connected to God—whether you are truly a child of God and truly belong to the church of Christ.
You see here how precisely the building upon the testimony of the apostles and prophets (see also Ephesians 2:20) will ensure you that, as a child of God, you know him as Father and the Son, Jesus Christ, as your Saviour. Without building your life upon this testimony, you are not truly connected to God. Then you are not sharing in what Jesus Christ, the Son of God, earned for you.
It is striking that John writes so very emphatically in this verse: his Son Jesus Christ. This also has to do with the erroneous doctrine that was introduced to the churches at that time. In this erroneous view, among other things, Jesus as human being was not regarded as the Christ. Jesus was not a human being and divine simultaneously. John emphasises that Jesus Christ, as he lived on earth as true God and man, is the Christ, the Saviour. This is indispensable and belongs to the faith of the people of God, namely those who have God as their Father. Only when you believe this of Jesus Christ is eternal life earned through Christ. John also makes it very clear close to the end of this letter, I write these things to you who believe in the name of the Son of God, that you may know that you have eternal life...And we know 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, (namely) in his Son Jesus Christ. He is the true God and eternal life
(1 John 5:13, 1 John 5:20).
When we read these verses, it is striking that John often speaks of Christ as the Son and of the believers as children of God. This makes it clear that we can only be children of God and can only know God as Father through Christ, the one who is truly the Son of God. He truly is the Son of God who earned eternal life on the cross for believers. In other places in the Bible, believers are also called sons of God (see, e.g., Romans 8:14, Romans 8:19; Romans 9:26; 2 Corinthians 6:18; Galatians 3:7, Galatians 3:26; Galatians 4:6–7; 1 Thessalonians 5:5). This is always with the distinction in mind, though, that Jesus Christ is the Son in a different way than we are sons of God. You can also see this difference when Christ appears to Mary Magdalene after his resurrection and says to her, “Do not cling to me, for I have not yet ascended to the Father; but go to my brothers and say to them, ‘I am ascending to my Father and your Father, to my God and your God” (John 20:17). Here the Lord Jesus is specifically not talking about our Father!
In the Heidelberg Catechism this is confessed in Lord’s day 13, question and answer 33: “Why is he [Christ] called God’s only-begotten Son, since we also are children of God?” Because Christ alone is the eternal, natural Son of God. We, however, are children of God by adoption, through grace, for Christ’s sake.
3 that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us; and indeed our fellowship is with the Father and with his Son Jesus Christ.