"The cross is the price and path of conversion. Because we are immersed in egoism and the tendency toward sin, the path of conversion to the following of Jesus is a path of repentance for sin and resistance against our own particular form of egoism." Segundo Galilea

For Peter and the disciples, the actuality of the cross was a stumbling block. That the Messiah had to die by crucifixion was incomprehensible to minds without faith. But the thief crucified with Jesus unknowingly received the grace of belief. Though he heard the crowd mockingly deride Jesus as the Son of God, though he saw the sign above Jesus' head decreed by Pilate, "Jesus of Nazareth, King of the Jews", he cried out in repentance, "Lord, remember me when you come into your kingdom." The cross was the path of conversion for him; it was the path to eternal  glory.  It is this same grace of faith that allows us to turn away from our sins and believe the Jesus as Lord and Messiah.