To add to the finished work of Jesus Christ is to disfigure it, mar it, and destroy it altogether. There is nothing you can contribute to the payment that Jesus made on the cross for sin. There is no penance you can undergo, no good work you can perform, no pilgrimage upon which you can embark, no punishment you can endure to clear your guilt before God. When Jesus said, ‘It is finished.’ he meant it. He meant that he had completely paid the price to release his people from their bondage to sin. So for you to try to pay for your own sins is to deny that Jesus really did finish paying for sin. For you to try to do something to earn your own salvation is to make Jesus Christ out to be a liar — James Montgomery Boice and Philip Graham Ryken "The Heart of the Cross"