This passage has some challenges. The first is that the King James Bible has an added part in verse 7 which most modern translations do not. This is due to variations in the ancient manuscripts.

The second problem is to understand what it means when it says Jesus came ‘by water and the blood’ (v6). There are different ideas about this but the most plausible answer I think is that they refer to Jesus baptism at the beginning of His ministry and His death at the end.

This would mean that the three who testify to Jesus are His baptism, His death and the Holy Spirit (v8). This means that it is Jesus’ ministry and His death along with the Spirit’s work in the person’s heart, convinces them of the truth of the Gospel.

The testimony of God is much greater than man’s (v9) and we can think of how God testified at Jesus’ baptism with the voice from heaven and the giving of the Spirit. We can think of how God testified at Jesus’ death through the darkness, the torn curtain and the resurrected saints. Christianity is faith, but it is not blind faith, it is based on God’s powerful testimony.