Then the eleven disciples went to Galilee, to the mountain where Jesus had told them to go. When they saw him, they worshiped him; but some doubted. (Matthew 28:16-17 NIV)
The belief in the resurrection wasn’t instantaneous even for some of Jesus’ early disciples who saw Him after He rose again and ascended to heaven. It took them a while to overcome the traumatic experience of witnessing His death on the cross. Even the old patriarch Jacob had trouble believing that his favourite son Joseph was still alive after having believed that he was dead for so long (Genesis 45:26).
So many people have been through terrible experiences that the belief in a resurrection seems unlikely to them. But it’s also to these people that God wants to reveal Himself and grant them His resurrection power.