Satisfying the Lawâ€™s Demand's and Curses
The second Adamâ€™s perfect holiness of human nature, and obedience of life to the precept of the law as a covenant, are as necessary to the justification of sinners as is His suffering of its penalty. The doctrine of justification by faith establishes the law, the whole law, the honor of the precept as well as that of the penal sanction. But this it could not do if it did not represent the righteousness of Jesus Christ as consisting in His active obedience as well as in His passive. Active obedience, strictly speaking, cannot be said to satisfy vindictive justice for sin. And, on the other hand, suffering for punishment gives right and title unto nothing, it only satisfies for something; nor does it deserve any reward, as John Owen mentions in his work on justification. Christâ€™s satisfaction for sin could not render His perfect obedience to the precept unnecessary; nor could His perfect obedience make His satisfaction for sin by suffering the penalty unnecessary, because it was not of the same kind. The one is that which answers the lawâ€™s demand of perfect obedience as the ground of title to eternal life; the other is that which answers its demand of complete satisfaction to divine justice for sin. The meritorious obedience of Christ to the precept could not satisfy the penal sanction; and the sufferings and death of Christ, could not satisfy the precept of the law. The commandment of the law as a covenant requires doing for life; the curse of that law demands dying as the punishment of sin. These, though they are never to be separated as grounds of justification, yet are carefully to be distinguished. The perfect obedience of Christ is as necessary to entitle believers to eternal life as His suffering of death is to secure them from eternal death. His satisfaction for sin, applied by faith, renders them innocent or guiltless of death; and His obedience makes them righteous or worthy of life (Romans 5:19). As the latter, then, is as necessary to complete their justification, according to the gospel, as the former, so it is as requisite as the former to establish the honor of the law.
Excerpt from A Treatise on the Law and Gospel by John Colquhoun