Jesus was raised from the dead on the third day after giving Himself as a sacrifice for our sins. But why did He not immediately return to heaven to be with the Father? There seems to be two answers to that question. He made post-resurrection appearances to His disciples to both convince them He was alive, and also to teach them the meaning of His death and resurrection so that they might be His witnesses (Luke 24:36-49).
On a number of occasions, Jesus told His disciples that He must be killed and be raised again from the dead, but He did not make clear why He must die until after the resurrection. In His post-resurrection appearances to His disciples, Jesus proved to them He was alive so that they could be confident witnesses to this fact (Luke 24:36-43). And as witnesses, they must also know and believe that Jesus died for their sins so that they might boldly proclaim to others that they too could be forgiven through His death and resurrection (Luke 24:44-49).