1. It shows them what Christ did and suffered.
The moral law is of special use to regenerate persons, or true believers, both as a covenant of works and as a rule of duty. In its covenant form, it serves to show them what Christ, the second Adam, did and suffered in their stead. By requiring from all who are under it – as the conditions of eternal life – perfect holiness of nature and perfect obedience of life, with complete satisfaction for sin, it teaches believers what the Lord Jesus, in the greatness of His astonishing love, condescended to become, to do and to suffer for them. They may see in it as in a glass that He did infinitely more for them than any mere man or angel could ever have done (Rom 8:3-4, Phil 2:8, Gal 3:13-14). Thus the law, in subservience to the gospel, teaches believers indirectly what the gospel teaches them in direct terms.
2. It shows them the vastness of their obligations.
It is of use also to show them what infinite obligations they lie under to the Lord Jesus for having fulfilled all the righteousness of it in their stead, Though they are not under the law in its covenant form to be either justified or condemned by it, yet it is of special use to them to teach them how much they are bound to love and serve Christ who, by obeying its precepts and enduring its penalties in their stead, has brought in everlasting righteousness for their justification. And so it is a means of exciting their gratitude to Christ, and also to God, who so loved them as to send Him to answer all its demands for them (2 Cor 9:15, Col 1:12-14).
The law as a rule of life is also of great use to believers. For although they are not under it as a covenant of works, either to be justified by it for their obedience or to be condemned by it for their disobedience, yet they are under it as the rule of their new obedience, and they count it their exalted privilege and pleasure to be so (1 Cor 9:21).
1. It shows them how far they are from perfection in holiness.
In this point of view, it serves, under the illuminating influences of the Holy Spirit, to show them how far they are from perfection of holiness. In order to render them more humble and contrite, to cause them to renounce, in a higher degree, all confidence in their own wisdom, righteousness and strength and to trust constantly and only in the Lord Jesus for all their salvation, the law shows them the sin that dwells in them and that cleaves to all their thoughts, words and actions. It is of great use to teach them their need to be more humble, penitent and holy. And so it serves, in a high degree, to promote their sanctification and their desire to attain perfection of holiness (Phil 3:10-14, Rom 7:22-24). As it requires them to be perfectly holy (Matt 5:48), it shows them that their lack of perfect conformity to it is, every moment, their sin, and that they ought continually to press on toward perfection and long for heaven, where their holiness and happiness will be perfect (2 Cor 5:2-4, Phil 1:23).
2. It supplies evidence of their sanctification.
It serves, under the witnessing of the Spirit, to evidence to their consciences the reality of their sanctification. The holy law serves as a touchstone by which believers may try, and so discover, their begun conformity to the image of the Son of God, the firstborn among many brethren. Comparing their hearts and lives with that standard, they sometimes perceive that, though they are far from having a perfection of the degrees of sanctification, yet they have a perfection of its parts. And so the law as a rule tends, in the hand of the Holy Spirit, to promote their comfort as well as their holiness. “Our rejoicing is this,” says an apostle, “the testimony of our conscience, that in simplicity and godly sincerity, not with fleshly wisdom, but by the grace of God, we have had our conversation in the world” (2 Cor 1:12).
As a covenant of works, the law is the instrument of the Spirit, as a spirit of bondage, for convincing and alarming secure sinners; but as a rule of life in the hand of the blessed Mediator, it is a means employed by the Spirit, as a Spirit of adoption, for comforting and encouraging true saints. Their habitual desire and endeavour, from faith and love and for the glory of God, to keep all its commandments, are a good evidence to them that they are the children of God and are conformed to the image of His Son.
3. It shows them what duties they owe to God.
It is of great use to show believers what duty they owe to their God and Redeemer, and to direct them how to perform it. Christ, whom the Father has given for a leader and commander to the people, gives to believers that law to be the rule of their obedience, to inform them what grateful service and what holy obedience they owe to Him, and to God in Him, and to direct them in the course of their obedience. Accordingly the holy Psalmist says, “Through Thy precepts I get understanding: therefore I hate every false way. Thy word is a lamp unto my feet, and a light unto my path” (Ps 119:104-105). The law as a rule directs them how to express their gratitude to the Lord Jesus for fulfilling it for them in its covenant form (Rom 8:3-5). It enjoins them to show their love and thankfulness to Him by a growing conformity of heart and life to it as the rule of their obedience (John 14:15, 1 Tim 1:5, Rom 12:1-2).
While it shows them what is good and what is evil, what they ought to do and what they ought to forbear, it guides them in the exercise of their graces and in the performance of their duties. No sooner does the law as a covenant urge men to Christ, for deliverance from the dominion of it in that form, than Christ leads them back to the law as a rule for the regulation of their heart and conduct, in order that they may, by their sincere obedience to it as a rule, express their gratitude to Him for His perfect obedience to it as a covenant in their stead (John 14:15).
4. It puts them under obligation to various duties.
Finally, it serves the highly important purpose of obliging the saints to all their various duties. The law as a rule of life to believers comes invested with infinite authority and therefore lays them under infinite obligations, even to perfect obedience. Seeing they do not cease to be creatures by becoming new creatures, they are, and ever will be, obliged to yield personal obedience to the moral law as a rule of life – by the sovereign authority of their Creator: the Father, the Son and the Holy Spirit. But this divine authority, as was hinted above, issues to them from the Lord Jesus, the great Mediator, who has created and redeemed them and who has all the fullness of the Godhead dwelling in Him bodily. They therefore receive the law at His mouth.
And surely the law can lose nothing of its original authority by being conveyed to them in such a glorious channel as the hand of Christ, for not only is He God over all, but all the sovereignty and authority of the infinitely glorious Godhead are in Him as Mediator (Ex 23:21). The Lord Jesus therefore, instead of dissolving, or in the smallest degree weakening, the moral law, does greatly strengthen its original obligation (Westminster Confession of Faith 19:5). Indeed, it is only to God as in Christ – only according to the law as in the hand of Christ – and only by a real believer in Christ, that the smallest acceptable obedience can be performed. The law as a rule in the hand of Christ is, then, of special utility to believers inasmuch as it shows them how high are their obligations to the love and practice of holiness. And thus it eminently subserves the gospel, that “doctrine which is according to godliness”.
[This article is taken, with slight editing, from A Treatise on the Law and the Gospel. Colquhoun (1748-1827) was minister of Leith and one of the best writers of his time in Scotland. It appeared with a number of earlier sections on the uses of the law in copies of this year’s Free Presbyterian Magazine from whence it has been taken with permission, while the headings have been introduced.]