Jesus had told his disciples that on the third day he would rise from the dead. The religious and Roman authorities had sealed the stone in place and stationed soldiers to guard the tomb to prevent anyone from stealing the body and claiming that Jesus was alive. So here was this huge stone to separate the living from the dead. What was inside the tomb was dead, and the stone was to insure that the dead body remained inside. Life is on the outside of the tomb.
Death is on the inside.
The stone separates them. Many people today live their lives as if they are already in a burial cave a tomb. Their lives are sad, depressed, fearful and discouraged. There is no joy, no life left in them. They are dead people walking.