No law can be set above God, but God Himself should never be thought of as utterly lawless. There are things He cannot do: "He cannot deny Himself" (2 Timothy 2:13). He "cannot lie" (Titus 1:2).
The reason He cannot do these things is not because some higher law binds Him, but because such actions are inconsistent with His own holy character.
Calvin wrote: "We fancy no lawless God who is a law unto himself. . . . The will of God is not only free of all fault but is [itself] the highest rule of perfection, and even the law of all laws" (Institutes 3.23.2).
To the careless thinker, it may seem as if Calvin was either contradicting himself or making an extremely fine distinction (God is not a law unto Himself; but His will is the law of all laws). Actually Calvin was making a crucial point. A proper understanding of biblical law ultimately hinges on this point: While acknowledging that God gives account to no one, we must likewise recognize that He is not lawless. The moral principles by which God rules, far from being aimless or arbitrary, are grounded in His own perfect holiness and are therefore as eternal and unchangeable as God Himself.
It is vital to see this aspect of the law. Unless you want to say that God is capricious, changeable, or even lawless, you cannot deny that certain eternally inviolable moral standards flow from His very character and not only determine the nature of the law by which He governs His creatures, but these principles also circumscribe God's own actions.
If you affirm that much, you have already in effect acknowledged the validity of a fundamental distinction between the moral and ceremonial aspects of the Mosaic code.