The three hours of darkness was a miracle. It was not an eclipse, because that would have been impossible during the Passover season when there is a full moon. It was a God-sent darkness that shrouded the cross as the Son of God was made sin for us (2 Cor. 5:21). It was as though all nature was sympathizing with the Creator as He suffered and died. When Israel was in Egypt, three days of darkness preceded the first Passover (Ex. 10:21ff). When Jesus was on the cross, three hours of darkness preceded