Robert Traill (The Lord’s Prayer, John 17:24), Works 2:245:
The law makes a representation of believers that they must not receive, but set Christ’s representation against it. Whoever seeth his own face in the glass of God’s holy law, seeth a hateful spotted face: For by the law is the knowledge of sin, Rom. 3:20. Now, if a believer think, that just as he seeth himself in this clear glass, so doth he appear in the presence of God, that were dreadful indeed. But there is another representation that Christ makes of them unto God, that the law knows not of. The more a man knows of the law, the more he knows of his own sin and danger. And this sad condition remains till he look beyond and above the law unto the righteousness of Christ, who hath satisfied and fulfilled the law by himself, and makes this over to a believer, and represents him to God, as clothed with it.
Westminster Confession of Faith, Chapter 19, Section 6:
Although true believers be not under the law, as a covenant of works, to be thereby justified, or condemned; yet is it of great use to them, as well as to others; in that, as a rule of life informing them of the will of God, and their duty, it directs and binds them to walk accordingly; discovering also the sinful pollutions of their nature, hearts, and lives; so as, examining themselves thereby, they may come to further conviction of, humiliation for, and hatred against sin, together with a clearer sight of the need they have of Christ, and the perfection of his obedience. It is likewise of use to the regenerate, to restrain their corruptions, in that it forbids sin: and the threatenings of it serve to show what even their sins deserve; and what afflictions, in this life, they may expect for them, although freed from the curse thereof threatened in the law. The promises of it, in like manner, show them God’s approbation of obedience, and what blessings they may expect upon the performance thereof: although not as due to them by the law as a covenant of works. So as, a man’s doing good, and refraining from evil, because the law encourageth to the one, and deterreth from the other, is no evidence of his being under the law; and, not under grace.
Herman Witsius, The economy of the covenants, volume 1, pp. 370:
The covenant of grace, or the gospel, strictly so called, which is the model of that covenant, since it consists in mere promises, prescribes nothing properly as duty, requires nothing, commands nothing; not even this, Believe, trust, hope in the Lord, and the like. But it declares, sets forth, and signifies to us, what God promises in Christ, what he would have done, and what he is about to do. All prescription of duty belongs to the law, as, after others, the venerable Voetius has very well inculcated. And we are by all means, to maintain this, if, with the whole body of the reformed, we would constantly defend the perfection of the law, which comprehends all virtues, and all the duties of holiness.
Source: https://www.puritanboard.com/threads/why-does-limited-atonement-matter.87650/page-3, Comment 71
“What purposes does the Law then serve?”
First, the Law helps to control violent outbursts of sin and keeps order in the world (a curb).
Second, the Law accuses us and shows us our sin (a mirror).
Third, the Law teaches us Christians what we should and should not do to live a God-pleasing life (a guide).
The power to live according to the Law comes from the Gospel.”
Source: Luther’s Small Catechism with Explanation (Saint Louis: Concordia Publishing House, 1991), qtd. at http://theaquilareport.com/three-uses-law-luthers-catechism/
Charles Hodge, Commentary on 2 Corinthians 3:6,
“The law, in every form, moral or Mosaic, natural or revealed, kills. In demanding works as the condition of salvation, it must condemn all sinners. But the gospel, whether as revealed in the promise to Adam after his fall, or in the promise to Abraham, or in the writings of Moses, or in its full clearness in the New Testament, gives life. As the old covenant revealed both the law and the gospel, it either killed or gave life, according to the light in which it was viewed. And therefore Paul sometimes says it does the one, and sometimes the other. But the spirit giveth life. The spirit, or the gospel, gives life in a sense correlative to that in which the letter (i.e. the law) kills. 1. By revealing a righteousness adequate to our justification, and thus delivering us from the sentence of death. 2. By producing the assurance of God’s love and the hope of his glory in the place of a dread of his wrath. 3. By becoming, through the agency of the Holy Spirit, an inward principle or power transforming us into the image of God; instead of a mere outward command.”
Source: https://www.puritanboard.com/threads/why-does-limited-atonement-matter.87650/page-2, Comment 51
Archibald Hall, A Treatise on the Faith and Influence of the Gospel, pp. 104-105:
“It is a capital mistake in this opinion, that the gospel is blended with the law; and upon the ruins of both the law and the gospel, a new mode of divine administration is contrived, under the name of gospel laws. The law and the gospel are entirely distinct from one another, and ought never to be confounded together. A gospel law is a contradiction in terms; for the works of the law and the grace of the gospel stand opposed to one another in the great concerns of our justification before God. To compound the sincere endeavours of men with the grace of God, is to destroy the perfection of the law, and to subvert the sovereignty of saving grace, at one bold stroke. If such a scheme be once admitted, the divine law will no longer exhibit the perfection of beauty that is essential to the eternal God; and the glorious gospel will no longer reveal the riches of his sovereign grace, whereby he has mercy on whom he will have mercy. This dangerous innovation sets aside the necessity of knowing and believing the truths of God, by resting the whole of a man’s salvation upon the sincerity of his intentions to please his Maker, whatever his principles may be; and it opens the door to licentiousness of practice, by representing the Lawgiver as demanding only that which is upright, not that which is perfect. Upon the whole, this doctrine concerning a new law is a gross perversion of Christianity.”
Source: https://www.puritanboard.com/threads/why-does-limited-atonement-matter.87650/page-2, Comment 48