The Jews object to Jesus saying that he came down from heaven. This would indicate His superiority to them which they would be unable to accept. Odeberg reveals the Jewish mind on the matter of the divine descending from heaven and joining to man:

“The Jews do not reject the idea that a man appearing on earth as an earthly being could be descended from heaven; they maintained that Elijah and other celestial figures appeared on earth and dwelt among men as earthly beings; (2) neither do they reject the idea, that a man, born of parents, of ‘woman’, of earthly ‘semen’, could receive a Divine calling, be a messenger from God, obtain revelations from the Divine world; (3) but they rejected the idea that a man born of earthly semen could at the same time be a celestial being, be of celestial origin, could have ‘descended from heaven’”

Morris 371

Their objections to Jesus’ statement seem to be verified by knowledge which they have at their disposal: they know his parents and He is of lowly descent; both of these, in their eyes, would indicate He came from earth, not from heaven. The irony of this is that if they really did know His true parents, it would prove to them the validity of His assertion.