They said therefore to him, "What then do you do for a sign, that we may see, and believe you? What work do you do?
II. Unbelief is contrary to man's nature.  Man's very nature is to believe, an inveterate trait locked into the deepest instincts of human life.  Evil men know that trait is in men and take full advantage of it, all of the schemes ever devised for defrauding men having as their dominant characteristic a reliance on man's willingness to believe almost anything. As P. T. Barnum indelicately stated it, "There's a sucker born every minute!"  What an incredible marvel it is, therefore, that in the contemplation of the mountains of evidence attesting the authenticity of Christ and his message, the behavior of mankind should be atypical.  What a wonder that people will not believe in God, but will believe in witchcraft! No wonder Jesus marveled at unbelief.