The questions and answers in this interchange between Jesus and the Jews closely resemble the talk between Him and the Samaritan woman in John 4, except there is a different conclusion. There Jesus talked of life using the figure of water, and here using the figure of bread. There the woman went back and forth between her good and evil impulses until her better nature triumphed. Here there was a similar vacillation, but the result was the exact opposite. (from McGarvey TFG 384)

How well this interchange proves the statement in 1 Co 1:22 which says that “the Jews require a sign.” There was a rabbinic saying that if a prophet gives “a sign and wonder then one must listen to him; but if not, then one need not listen to him.” (qt’d in Morris 362) Jesus had already given them signs but all they saw were miracles. As Dodd points out, to John a sign “is not, in essence, a miraculous act, but a significant act, one which, for the seeing eye and the understanding mind, symbolizes eternal realities.” (qt’d in Morris 362) The Jews were fresh from seeing and experiencing the miracle of the feeding of the 5000 the day before, and yet they still demanded a sign.

“see it and believe you” = puts their priority on sight. They kept thinking that if only they could see another sign or witness some more evidence, then they would believe. It is the same with people today, but why? If it is not lack of evidence which keeps them from believing, then what does?