Now, as a preacher I don't think that Jesus was a great outstanding forceful preacher. John the baptist was a preacher, but he done no signs at all. He never performed a miracle.
But Jesus come by not preaching so forceful as John, but there were signs and wonders accompanying Him. He said, "If you can't believe Me believe the works that I do. If you can't believe Me believe the a vindication that the Father has given of Me, for the works that I do, the same testify that the Father has sent Me." What a statement.
Think of it. "The works that I do testify that the Father has sent Me." Man can make any kind of a statement, but if God don't back that statement up, you've got a right to say it's wrong. But when God comes around and confirms that statement to be the truth then it's sin to disbelieve it. For what is sin? Sin is one thing: "unbelief."