On the Law and Gospel distinction

"Since true believers are already irrevocably interested in the covenant of grace, in the righteousness of Christ, and in favor of God; and since they have in Christ, and on the ground of His righteousness imputed to them, a complete security against eternal death and a full title to eternal life; the law as the law of Christ has no sanction of judicial rewards or punishments. It has no promise of eternal life or threatening of eternal death annexed to it. The form of the covenant of works, indeed, is eternally binding on all who live and die under that violated covenant, but because Christ, as last Adam, has answered all the demands of it for believers, they are delivered from the law in that form (Romans 7:4-6).
The law which believers are under is the law of Christ, and of God in Christ, which has no promise of eternal life to them for their obedience to it. The promise of eternal life to the saints is the promise of the covenant of grace or the gospel, and not of the law, as a rule of duty. Eternal life is promised to them not in consideration of their sincere obedience to the law as a rule of life, but on account of Christ's perfect obedience to it as a covenant of works received by faith and imputed by God. It is promised to them not as a reward of debt for their sincere obedience, but as 'the gift of God through Jesus Christ our Lord' (Romans 6:23). The righteousness of Jesus Christ imputed to them gives them a perfect title to life; they are already heirs of it, 'and joint heirs with Christ.' They have begun possession of it, and have the gracious promise of the gospel that they shall, in due time, attain thr perfect and everlasting possession." - John Colquhoun, A Treatise on the Law and Gospel.