We are sure ... - See a similar confession of Peter in Matthew 16:16, and the notes at that place. Peter says we are sure, in the name of the whole of the apostles. Jesus immediately cautions him, as he did on other occasions, not to be too confident, for one of them actually had no such feelings, but was a traitor.
Related Commentaries of John 6:69
John 6:69
69 And we believe and are sure that thou art that Christ, the Son of the living God.