Question: Is the law of the ten commandments equivalent to the covenant of grace, or is it a compendium of this covenant?
Answer: The covenant established at Horeb prior to the giving of the law is truly the covenant of grace; however, we deny that the law of the ten commandments is the covenant of grace or its compendium. This is evident for the following reasons:
First, the entire contents of the law of the ten commandments was perfectly impressed upon the nature of Adam, and this law would have, if his transgression had not interfered, been passed on perfectly to his descendants. After the fall, the law is yet impressed upon the hearts of the heathen, although imperfectly (cf. Rom 1:19-20; Rom 2:14-15). If, however, the law were a compendium of the covenant of grace and equivalent to the covenant of grace itself, it would already have existed prior to the fall, and the covenant of grace would have been naturally known to the heathen apart from the gospel. This is absurd, and thus also that the law is equivalent to the covenant of grace.
Secondly, the law is the requirement and condition of the covenant of works, life being promised upon personal obedience to the law: ―Do this and thou shalt live.‖ Whatever is identical to the covenant of works in its demands and contents cannot be equivalent to the covenant of grace. For where the law says: ―Do this and thou shalt live,‖ the covenant of grace says: ―Believe in the Lord Jesus Christ and thou shalt be saved.‖ These two covenants are too distinct from each other, and the one covenant negates the other (Rom 10:5-6; 11:6).
Thirdly, Christ is the Surety of the covenant of grace who therefore must be included in a description of this covenant; it cannot be understood apart from the knowledge of Christ. However, in the law there is not a word regarding a Surety, or regarding faith in the Surety, Jesus Christ. Therefore, the law is not equivalent to the covenant of grace.
Fourthly, the covenant of grace is efficacious unto the regeneration, justification, and salvation of man; however, the law is not efficacious unto regeneration, justification, and salvation. ―If there had been a law given which could have given life, verily righteousness should have been by the law‖ (Gal 3:21); ―For if the inheritance be of the law, it is no more of promise‖ (Gal 3:18); ―For what the law could not do, in that it was weak through the flesh, God sending His own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh‖ (Rom 8:3). Yes, those who are under the law are under the curse (Gal 3:10); the law is therefore not equivalent to the covenant of grace.
Fifthly, the covenant of grace only makes promises—also the inscription of the law in the heart (cf. Jer 31:33; Ezek 36:26-27). The law, however, only demands and has no promise, except upon the condition of perfect, personal obedience—a promise which cannot be fulfilled by anyone after the fall as no one is able to fulfill the condition. The law demands but does not promise any efficacy. The law is therefore not equivalent to the covenant of grace.
–The Christian’s Reasonable Service, vol.3, pp.45-46