The idea that Jesus died for our sins could only have come about after Jesus had actually died.  Nobody involved in his crucifixion believed that his death would undo the damage of sin.  His followers never anticipated his death with the expectation of salvation.  That would have been ghoulish.  These beliefs were formed after the death of Christ.  So why do Christians accept these ideas as though from God?  

The belief that Jesus died for our sins arouse within the Christian community following the death of Jesus.  Only Jesus was God.  These people left making sense of his death were ordinary human beings.  So why do Christian churches teach the story of salvation as having come from God?

Every story has an author. Who wrote the story that Jesus died for our sins?

And who wants us to believe that this is so?