The Law must have its righteous requirements of perfect righteousness met. Without the fulfillment of the righteousness of Christ to fulfill the Law for us we would have to die for every sin and even our every good work that was not covered by the imputed righteousness of Jesus. Thus all are saved by a work that was accomplished in Christ Jesus and not by our fulfilling the righteous requirements of the Law. This mercy and grace and love and forgiveness which God has revealed to us through the gospel will break the heart of all who believe the gospel and will motivate us to love and serve our God and our fellow man. The more we trust in the imputed righteousness of Christ, the more we will receive the Holy Spirit to enable us to serve as God's friend rather than as a slave trying to earn our salvation by our good works of obedience.
True sanctification can now spring from the converted heart of a repentant sinner.
Thus we serve God from a heart overflowing with gratitude for the great sacrifice which He has made for us in humbling Himself and coming into the world to walk among us and finally to be crucified as a guilty criminal in our place. This is the whole theme of the New Testament. If the Biblical concept of forensic justification by grace alone through faith alone in the imputed righteousness of the Sinless One, Jesus Christ alone is in any way lost sight of by the Church, all that is left is a humanistic moralism of salvation by a moral change within the heart of man. This is the very basis of the Roman Catholic system of justification by imparted righteousness. The great breakthrough of the 16th century Protestant Reformation was the restoration of the primacy of justification by faith in the imputed righteousness of Christ as the sinner's assurance of eternal life.