Looking in the gospel of John, there are those who testify about Jesus. There is Jesus. That is one. There is the Father (ch 8, ch 10). That is two. So far these are two testimonies required by the Law of Moses. Then the Lord Jesus foretells the coming of the Holy Spirit, who will testify about Jesus. So that is three. Now the Law truly is well satisfied. But wait, there are more. There are the apostles who also must testify. So that is at least fifteen. Fifteen witnesses. Plus the disciples and close family of Jesus who may also testify. Plus the later disciples, the number goes up and up. All are united in Jesus. All are one. All agree in their support for the truth they know and believe, that Jesus is truly the Son of God, sent into the world by God the Father to give light to the world. So the gospel of John ends with the statement that many can testify that this gospel is true. I can testify too. It proves to be true in my own experience. I am not coerced into saying this, it is my truth, my own experience. More and more know it. More and more are one in saying it. The Father is God and Jesus is the Son of God.
