1 John 5:9
 If we receive the testimony of men, the testimony of God is greater, for this is the testimony of God that he has borne concerning his Son. (ESV)
Those who reject Jesus have to ignore the testimony of both men and God. The Apostle John himself is one who wrote of his eye witness testimony to Jesus. He walked with him on this earth for three years. In fact, John was such a great witness of all that Jesus did he wrote specifically about how much he had witnessed in the Gospel he wrote. Hear John's words:
 This is the disciple who is bearing witness about these things, and who has written these things, and we know that his testimony is true.  Now there are also many other things that Jesus did. Were every one of them to be written, I suppose that the world itself could not contain the books that would be written. (ESV)
In a three year span, John had seen Jesus do so many things that he claims that if books were written of all of them the world could not contain them. Of the 12 disciples who followed Jesus there were three that were in His inner circle, Peter, James, and John. Of those three, John was the closest with Jesus and was referred to as "the disciple that Jesus loved."
John writes to us that you can receive the testimony of men. And that testimony is great. It includes his testimony, as well as many others who have given testimony. The fact is, the whole world was turned upside down by Jesus Christ. It continues to be. And while the testimony of man is great, God's testimony is even greater! He has revealed himself to us in his Word and by His Spirit.
What have you heard about Jesus? Have you believed the testimony of men, even godly men? Consider also the testimony of God himself. He wants you to know him and to glorify his son.