First, the law and gospel consent: first, in the author--of both which is God; second, in their general matter, for both require justice and righteousness to salvation; third, in their end, namely the glory of God.
Second, they dissent in six things:
- The moral law is written in nature by creation; yes and since the fall we have some remainder of it in us. Romans 2:15, "the Gentiles show the effect of the law written in their hearts." But the gospel is not in nature, but above the reach of nature created, much more corrupted. The ground of the law is the image of God; but the ground of the gospel is Jesus Christ.
- The law will have us do something that we may be saved by it, and that is to fulfill it. The gospel requires no doing of us, but only believing in Christ. Objection: But believing is a work to be done. Answer: The gospel requires it not as a work to be done, but as it is an instrument, and the hand of the soul to lay upon Christ, Rom. 4:5; 3:21; 10:5. Hence it is that the law requires righteousness inherent; but the gospel, imputed.
- The law is propounded to the unrepentant sinner to bring him to faith; but the gospel to the believer, to the begetting and increase of faith.
- The law shows sin, accuses and reveals justice without mercy; but the gospel covers sin, and is a qualification of the rigor of the law. The law says, "Cursed is everyone, etc." The gospel qualifies that, and says, "Except he believe and repent, every man is accursed." Thus the law which manifests justice is moderated by the gospel, which mingles mercy and justice together: justice upon Christ, mercy unto us.
- The law tells us what good works must be done; the gospel, how they must be done. The former declares the matter of our obedience, and latter directs us in the manner of obeying...
- The law is no work of grace and salvation, no not instrumentality, for it is a ministry of death; the gospel preached works grace only, though the law may be a hammer to break the heart and prepare the way to faith and repentance.
The Papists, who hold that they [law & gospel] are one doctrine only, but herein differ: that the law is more dark, and the gospel more plain, the former more hard to fulfill, the latter more easy; that [law] is as a root of a tree, this [gospel] as the body and brances, by which premises they would conclude Christ to be no savior, but an instrument rather for us to save ourselves by, he giving us grace to keep the law. For a sinner must needs be saved by works, if there be no difference between the law and the gospel, and if the law which requires works were not moderated by the gospel, which requires not works, but faith.
William Perkins, The Workes: Commentary on the Epistle of Jude Vol. III (John Legatt: London, 1618) 495-6.