John testified about Jesus. "John, and he has testified to the truth"

Moses (and the propets) testified about Jesus "Moses .... for he wrote about me"

But must importantly the works that Jesus did and does testify about Jesus. "the very works that I do, testify about me"

The miracles that he performed, the things he said, the way he acted, the qualitiies he displayed and also the way people acted toward him all show that he came 'from the Father'.

In the last 2 thousand years we can see what a tremendous impact his life has had on the people of the world - this for me certainly testifies that he was 'from God'.

Also the effect that I see he has inside peoples lives around me (and my life) certainly testifies that he is the Son of God.