John encourages his readers to remain loyal to Jesus. Their congregations had been infiltrated by false teachers. The erroneous teaching had been connected to their opinion of Jesus as to who he was and what he had done. Presumably the false teachers were still spreading their views in the public arena, which meant that the public would have been informed of at least two different opinions about Jesus – there was the opinion of the Christian church and there was the opinion of the false teachers. Therefore, John proceeds to remind his readers who Jesus is and how they have come to have this knowledge. This is a reminder that is not enough to say that we are bearing witness to Jesus – we also have to make it clear concerning which Jesus we are bearing witness.
In describing Jesus, John uses terminology that may appear unusual to us when he says that Jesus ‘came by water and blood’. What does John mean? First, we can say that they were the means by which he made his journey, which was to become our Saviour. When we travel on a journey we all recognise milestones – the water and the blood refer to milestones in the life of Jesus. Is there an event in the life of Jesus that can be classified as him coming by water? The obvious event is his baptism when he began his public ministry. Is there an event in his life that can be classified as him coming by blood? The obvious event is his sufferings on the cross which climaxed his public ministry.
In order to appreciate John’s point, we have to recall what the false teachers taught. They agreed that Jesus came by baptism, that he had made a public announcement at the beginning of his three years of ministry in Israel. However, they did not want to speak about his death, which they regarded as a defeat. John obviously disagreed with their emphasis and insisted that the true Jesus, to whom we must be bear witness, is the Jesus who was crucified at Calvary, and who died on the cross as the sinbearer.
Of course, that ancient heresy as long since disappeared. Nevertheless, we are still called to testify to the crucified Jesus because the value of his death is still contested today. Many people are willing to have a Jesus who gave profound teachings and who lived as a good example, which is almost the same as saying that he came by baptism. Such a testimony is not half-correct, rather it is a complete distortion of who Jesus is and why he came. We have to tell all the truth about Jesus.