Getting our definitions straight is a necessary bit of throat-clearing before we get into the argument at hand. By law I mean the process that produces and sustains the formal and public rules by which we attempt to order our life together. Law is legislating, adjudicating, administering and negotiating the allocation of rights and duties, in the hope of preventing harm, resolving conflicts, and creating means of cooperation. So I am obviously speaking of law in a quite comprehensive sense.
As for transcendence, a number of other terms might be employed. We might speak of the ontological or metaphysical basis of law. Or, in the more classical tradition, we might prefer to speak of a hierarchy of goods from which law is derived and to which law is accountable. Whatever terminology we choose to employ, the point is that the law and laws are not self-legitimating. In fact, the very term “self-legitimating” is a nonsense term. Something can only be declared legitimate by reference to something else. Indeed, at the risk of seeming pedantic, it should be noted that the adjective “legitimate” is from the past participle of legitimare which means to make legitimate, and has as its first meaning to be lawfully begotten.