From Seeing and Savoring Jesus Christ, by John Piper:

God raised Jesus Christ from the dead. Everybody knew he was dead, from the governor to the executing soldiers to the women who buried him to the adversaries who feared a conspiracy of resurrection rumor. They all knew he was dead. That is why the fabrication concocted to explain the empty tomb was not that he wasn't really dead, but that the disciples stole the body. But it didn't work, because people don't risk their lives for a self-made falsehood. The body was not in the tomb, otherwise the enemies would have put a stop to Christianity with Jesus' remains. The disciples were ablaze with boldness, risking their lives by preaching that Jesus was alive. The evangelist Stephen and the apostle James lost their lives. And for forty days Jesus was appearing to individuals and groups, some as large as five hundred. Most of these were not gullible, but hard to convince.

As the possibility dawned on the skeptical disciples that the resurrection might be true, the first speculation was that the Jesus they saw was a ghost or apparition of some kind. But Jesus was ruthless to abolish this speculation immediately. To doubting Thomas he said, "Put your finger here, and see my hands; and put out your hand, and place it in my side. Do not disbelieve, but believe." And before the the stunned disciples on another occasion, Jesus insisted on eating fish to show them that he was not a ghost.