Pilate was a coward. He was afraid of Caesar, his boss in Rome, who would deal with him most severely if he failed to maintain law and order.  Pilate’s record was not good.  He had incited riots and tried to put down rebellion by killing Galileans, forcibly entering the Temple and adding their blood to the sacred sacrifices (Luke 13:1).  He was therefore afraid of the religious leaders who had incited a mob to demand the death of Jesus.  Three times, Pilate tried to appeal to Roman law, protesting that Jesus had not broken any of the rules; but in vain.  The crowd was at fever pitch in screaming for the death of Jesus.  And yet, only a few days earlier they had been shouting His praise (John 12:13), just as Jesus had predicted (Luke 13:35).  

However, Pilate could see a cowardly way out.  His 'Passover peace-present to the people' was to release one prisoner of their choice.  Barabbas was a terrorist who was on 'death row'.  So, Pilate encouraged the crowd to allow Barabbas to be set free.  But that did not satisfy the crowd either.  They wanted Jesus to take the place of Barabbas ... and eventually Pilate agreed.  How cowardly!

But how full of meaning!  Barabbas means 'son of the father'!  Jesus Christ was the Son of Father God, and He chose to become the substitute for every convicted criminal, indeed every person who has broken God’s laws .... how courageous!  That substitution was to happen at Passover when the nation sacrificed a lamb, remembering how a lamb's blood shielded the ancient Israelites from God's wrath in Egypt (Exodus 12:1-29).  As John the Baptist had said a few years earlier, "Look, the Lamb of God, who takes away the sin of the world!" (John 1:29).
 
Jesus was the substitute for us on the cross.  As Isaiah 53:4-6 says, "Surely he took up our pain and bore our suffering, yet we considered him punished by God, stricken by him, and afflicted.  But he was pierced for our transgressions, he was crushed for our iniquities; the punishment that brought us peace was on him, and by his wounds we are healed.  We all, like sheep, have gone astray, each of us has turned to our own way; and the Lord has laid on him the iniquity of us all."  If you believe that and have welcomed Jesus as your Saviour - then your sins have been punished, your guilt is taken away, your shame has been removed and you have become a child of God.  So rejoice and do not be cowardly, but tell the world that Jesus is the only substitute for sin, and urge them to believe in Him.