Luke 16:31 (NIV)
If they did not listen to Moses and the prophets, they will not be convinced even if someone rises from the dead.
This pretty much sums up the stubbornness of the people during Jesus's time. They demanded signs and wonders, and when the same were given they refused to believe! Faith that depends on signs and wonders is no faith at all. If one doesn't believe Jesus because of who He is then they'll never believe even if they witnessed His miracles. May we never commit this unpardonable sin.