Jeffrey, Ovey and Sach provide a wonderful definition of penal substitution. Here is why Jesus came. “The doctrine of penal substitution states that God gave himself in persons of  his Son to suffer instead of us the death, punishment and curse due to fallen humanity as the penalty for sin. . . .  God the Holy Trinity thus turned aside hs own righteous wrath against sinful humanity; endured and exhaueted the curse of the law that stood against us; cleansed us of our sin and clothed us in Christ’s righteousness; ransomed us from our slavery to sin, the world and the devil by paying our debt, cancelling the devil’s power of  accusation against us, and liberating us to live new lives empowered by the Spirit; triumphed over all evil powers by punishing evil in the person of the Son; and reconciled us with himself by removing the barrier of sins and enmity between us; in order that we may stand blameless and forgiven in his glorious presence, credited with the perfect righteousness of the Lord Jesus Christ, as adopted children of God, gazing upon his face for all eternity. God vindicated his  truthfulness by remaining faithful to his promise that sin will be punished; he maifested his justice by punishing sin and acquitting the righteous; he gloriried his name by exalting his Son and placing all things under his feet; and he demonstrated hs love by dying for sinners and reconciling to himself those who were once his enemies” (p. 104).