This is the disciple that beareth witness of these things, and wrote these things: and we know that his witness is true.

This is the disciple who testifies to these things and who has written them down. And we know that his testimony is true.

this is the disciple who is testifying concerning these things, and he wrote these things, and we have known that his testimony is true.

This is the disciple who bears witness concerning these things, and who has written these things; and we know that his witness is true.