From Wolfhart Pannenberg, Metaphysics and the Idea of God, T&T Clark, (1988), 28-29:
I am skeptical of the claim that with the notion of highest perfection we have already reached the idea of God. The idea of God, however construed, has a considerably higher specification than is inherent in the general picture of a being with maximal perfection. For the idea of God cannot be separated from the elements of personality and of a will. It follows that the notion of a highest perfection as such is not yet identical with the idea of God. Of course, if we have arrived at the idea of God on other grounds, and if we then form the conception of a being with maximal perfection - and if, in addition, we raise the question of whom we should affirm this highest perfection - then in such a case it must be clear that this attribute can be affirmed only of the one God. It is in this sense that we are to understand Anselm's thesis that God is the being "greater than which none greater can be conceived". This sentence does not define the idea of God but already presupposes it and predicates of it the highest perfection.
