So, too, this doctrine of the Law is needful for believers, in order that they may not hit upon a holiness and devotion of their own, and under the pretext of the Spirit of God set up a self-chosen worship, without God's Word and command, as it is written Deut. 12:8,28,32: Ye shall not do ... every man whatsoever is right in his own eyes, etc., but observe and hear all these words which I command thee. Thou shalt not add thereto, nor diminish therefrom.
For the old Adam, as an intractable, refractory ass, is still a part of them, which must be coerced to the obedience of Christ, not only by the teaching, admonition, force and threatening of the Law, but also oftentimes by the club of punishments and troubles, until the body of sin is entirely put off, and man is perfectly renewed in the resurrection, when he will need neither the preaching of the Law nor its threatenings and punishments, as also the Gospel any longer; for these belong to this [mortal and] imperfect life. 25] But as they will behold God face to face, so they will, through the power of the indwelling Spirit of God, do the will of God [the heavenly Father] with unmingled joy, voluntarily, unconstrained, without any hindrance, with entire purity and perfection, and will rejoice in it eternally.
Solid Declaration, FC 1580