A great quote from D.A. Carson on Matthew 27:42:

The words “Let him come down from the cross, and we will believe in him” (Matthew 27:42) have several levels of meaning. They constitute a malicious barb directed at Jesus’ helplessness, while having the effrontery to suggest that the leaders’ failure to believe was his fault. The taunt piously promises faith if Jesus will but step down from the cross; but the reader knows that, in the mystery of providence, if Jesus did step down, there would be no “blood of the covenant for the forgiveness of sins” (26:26-29), no ransom (20:28), no salvation from sin (1:21), no theological basis for healing (8:16-17), no gospel of the kingdom to be proclaimed to nations everywhere (28:28-10), no fulfilment of Scripture. (D.A. Carson, Matthew p577)