"-what we have seen and heard we proclaim to you also, so that you too may have fellowship with us; and indeed our fellowship is with the Father, and with His Son Jesus Christ." 1 John 1:3
Against the charges of Christ merely apprearing to be a man by a group called the Docetists, John offers the proof of witness to refute their falsehood. He offers, both in the Gospel of John as well as 1 John, the fact that he had heard, seen, watched attentively and touched the very Son of God and that he was not the only one to do so.
Then as now, matters are settled on the testimony of witnesses. It should be understood that there was a high threshold in official matters. Matthew 18:16 reveals that an acceptable burden of proof is established in the mouths of two or three witness. The humanity and diety of Christ was proven through the witness by God, the Holy Spirit and John the Baptist at his baptism, by Jesus himself and by the more than 500 to whom he appeared after his ressurection.
Beloved, today we do not have the pleasure or privilege of experiencing the physical Jesus as those did who lived 2000 years ago but we believe by faith. That faith was made possible through the mouths of those who did experience him. This should not be as foreign a concept as some would make it out to be. The same individuals who will not accept Christ because they cannot see or touch him today will accept as fact the words of witnesses in legal, legislative, news and even gossip matters. They should know that they are not the first to take this position. The apostle Thomas refused to accept the witness of his peers and brothers in the faith, declaring that he would have to see for himself. As it would happen, Jesus showed up and said to Thomas, "Because you have seen Me, have you believed? Blessed are they who did not see, and yet believe” John 20:29. Those same witnesses and the Lord himself have said that he will one day likewise appear to us all.