The chief priests also, along with the scribes and elders, were mocking him, saying, "He saved others; he cannot save himself. He is the King of Israel; let him come down from the cross now, and we will believe in him.

"Let him come down from the cross now, and we will believe in him."

No doubt there are some issuing that taunt who had been a witness to one of Christ's many miracles or knew someone who was.  If those miracles were not sufficient for them then neither would his coming down from the cross be.  So in effect such taunts and demands of God - and who has never made them? - are in the end simply a way of absolving one from the necessity to believe.

Christ cannot come down from the cross for two reasons.  First, it would be the end of our salvation which he came to accomplish.  Second, it would be faith by coercion and thus the end of our free will.  Christ said "when I am lifted up from the earth, I will draw all men to myself," (John 12.32) - he draws men.

Christ never responded to demands for miracles (Matthew 12.39; 16.4).  He often did respond to requests for miracles made from a simple faith for some other purpose than to see tricks, such as the healing of a loved one.  As a possible example of an interior progression in this regard meditate on the healing of the official's son in John 4.46-53.

Finally we have the testimony of Abraham speaking from heaven: "If they do not listen to Moses and the prophets, neither will they be convinced even if someone rises from the dead." (Luke 16.31)