The breastplate of righteousness is God’s seal of approval upon a believer. When we accept Christ through faith, God approves of us because He approved His Son.  As a result we should live our lives to please God.  By living a holy life we prevent Satan’s success because we are focused upon God and His standard; we are living set apart! What better way to thwart the attacks of the enemy then to not give him a foothold in our lives to begin with?