Excerpt from “A Treatise on the Law and the Gospel” by John Colquhoun pages 260-261
All who are united to Christ, and justified for His righteousness imputed to them, are dead to the law as a covenant [of works]; not that they may be without law to God, but that they may be under the law to Christ; not that they may continue in disobedience, but that they may be inclined and able to perform sincere obedience in time, and perfect obedience through eternity, to the law as a rule of life. One design of their being delivered from the obligation of the law in its federal form is that they may be brought under the eternal obligation of it as a rule of duty in the hand of the adorable Mediator. Divested of the form of a covenant of works to believers, and invested with that of the covenant of grace, it stands under the covenant of grace as the law of Christ, and as the instrument of government in its spiritual kingdom, enforced by all its original and immutable authority. It loses nothing of its original authority by its being conveyed to believers in such a blessed channel as the hand of Christ since He himself is God over all, and since the majesty, sovereignty, and authority of the Father, the Son, and the Holy Spirit are in Him as Mediator (Exodus 23:21).
Indeed, it behooved the law of the Ten Commandments, inasmuch as it is the substance of the law of nature, a delineation of God’s moral image, and a transcript of His unspotted holiness, to be a perpetual and unalterable rule of conduct to mankind in all the possible states and circumstances in which they might be placed. Since God is unchangeable in His moral image, nothing but the entire annihilation of every human being can divest his holy law of that office. Its being an immutable rule of duty to the human race does not in the least depend on its having become the matter of the covenant of works. Whatever form it might receive, whether that of the covenant of works, or that of the covenant of grace, still it could not but continue an authoritative rule of conduct. No form, no covenant whatever, could at any time lessen its high obligation as a rule of duty on the reasonable creature. As the form of the first covenant was merely accessory to the moral law, so the law continues, and will forever continue under that form as the rule of duty to sinners, even in the place of torment. And as the form of the second covenant is also accessory to it, so it will remain eternally under this form, the rule of life, to saints in the mansions of glory.
Exodus 24