Believers Need the Law

But since believers are not completely renewed in this world, but the old Adam clings to them even to the grave, there also remains in them the struggle between the spirit and the flesh. Therefore they delight indeed in God’s Law according to the inner man, but the law in their members struggles against the law in their mind; hence they are never without the Law, and nevertheless are not under, but in the Law, and live and walk in the Law of the Lord, and yet do nothing from constraint of the Law.

But as far as the old Adam is concerned, which still clings to them, he must be driven not only with the Law, but also with punishments; nevertheless he does everything against his will and under coercion, no less than the godless are driven and held in obedience by the threats of the Law (1 Co 9:27; Ro 7:18–19).

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:

You shall not do according to all that we are doing here today, everyone doing whatever is right in his own eyes…. Be careful to obey all these words that I command you,… [but] everything that I command you, you shall be careful to do. You shall not add to it or take from it. (De 12:8, 28, 32).

Formula of Concord, Solid Declaration VI, 18–20