John 2:18 - Ellicott's Commentary On The Whole Bible

Then answered the Jews. — Comp. for the meaning of “the Jews” John 1:19; and for their question, Matthew 21:23. The Mosaic legislation contained a warning against the efficiency of the test by signs (Deuteronomy 13:1-3), but it was of the essence of Pharisaism to cling to it (Matthew 12:38; 1 Corinthians 1:22). It supplied an easy means of rejecting the moral conviction. A sign can only be evidence to the mind open to read the underlying truth. For “an evil and adulterous generation” it has no voice, and they can, after the feeding of the thousands, still demand “What sign showest Thou?” (John 6:30). There are bigots of incredulity. Knowledge is dependent upon action and will (comp. John 7:17). There is a mental condition which no evidence can convince, for it can always demand more. “If they hear not Moses and the Prophets, neither will they be persuaded, though one rose from the dead” (Luke 16:31).