Sanctification is the gracious work of God whereby those whom He has justified are renewed in the whole man after the image of God, set apart from sin unto holiness, and enabled more and more to die unto sin and to live unto righteousness. It is to be distinguished from justification, with which it is inseparably joined: justification is God’s act of declaring the sinner righteous, instantaneous, complete, and grounded wholly in the imputed righteousness of Christ; sanctification is God’s work of making the believer holy, progressive, never complete in this life, and worked out within him by the Spirit. The one changes a man’s standing, the other his state; the one is perfect at once, the other grows by degrees. Sanctification has both a definitive and a progressive aspect. Definitively, every believer is at conversion set apart and made holy in principle, the old man crucified with Christ, the reign of sin broken, so that the saints are called ‘sanctified in Christ Jesus’ from the outset. Progressively, the believer is then transformed by degrees, growing in grace, mortifying sin and quickening holiness, conformed increasingly to the image of Christ from glory to glory. It is wholly the work of God—it is God who sanctifies, the Spirit who renews—yet it is not passive in the believer, who is commanded to work out his own salvation with fear and trembling, to cleanse himself from all filthiness, to pursue holiness, precisely because it is God who works in him to will and to do. Thus sanctification is neither a mere human striving (legalism) nor a passive ‘letting go’ (quietism), but the Spirit-empowered, faith-fueled, lifelong pursuit of holiness, in which God works and the believer, by His grace, labors. Its end is perfect conformity to Christ, attained only at glorification, when the saints, made perfectly holy, shall see Him as He is and be like Him forever.