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.
Hence we may see, if Christ be given for a covenant of the people, that the gospel strictly and properly taken, is a bundle of good news, glad tidings, and gracious promises; our text is a sum of the gospel, and it is a free promise, “I will give thee for a covenant of the people:” there is no precept nor commandment here. The law is properly a word of precept, but not the gospel: the law commands all, and the gospel promises all. It were a disparagement to the divine law, if it were not perfect and exceeding broad, if there were any duty we are called unto not enjoined therein.
The unbeliever is already condemned in the gospel-court. Now, do not mistake this way of speaking, as if, when I speak of the gospel-court, I meant, that the gospel, strictly considered, condemned any man: the gospel, like its glorious Author, “comes not into the world to condemn the world, but that the world, through” it, “might be saved.” Neither do I mean, as if there were new precepts and penalties in the gospel, considered in a strict sense, which were never found in the book or court of the law. This is an assertion which has laid the foundation for a train of damnable and soul-ruining errors; as of the Antinomian error, in discarding the whole moral law as a rule of obedience under the gospel; the Baxterian error, of an evangelical righteousness different from the imputed righteousness of Christ; the Pelagian and Arminian error, of a sufficient grace given to every man that hears the gospel, to believe and repent by his own power.
For if this be so, then inevitably we must first obey Christ as a king, by repenting and believing, in order to our being justified by him as a priest; besides many other dangerous consequences which are unavoidable upon this new law-scheme. All which are avoided, by teaching, with the strain of orthodox divines, that there are no precepts in the gospel strictly taken; and that Christ in the gospel gives no new laws, but enforces the old law, namely, the moral, which being adapted to the gospel-dispensation, obliges us to believe in Christ upon his being revealed to us in the gospel, and consequently to repent also in an evangelical manner. For that these duties of faith and repentance, as to their essence, are required in the very first commandment of the moral law, is indisputably evident; and I do think it strange, to find it controverted by any who embrace and own the doctrine of the church of Scotland, particularly the Larger Catechism, where that point is plainly determined, in the explication of the foresaid first commandment.
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.
Thomas Watson, Body of Divinity (1838 ed.), p. 323:
The moral law requires obedience, but gives no strength, as Pharaoh required brick, but gave no straw; but the gospel bestows faith on the elect; the gospel sweetens the law, it makes us serve God with delight.