I have been trying to explain to a FaceBook friend how one can "have it both ways", regarding Plato's Ethryphro Dilemma.
1. Ethics is not imposed on moral agents extrinsically by any kind of Divine whimsy. The moral Law is not "positive" or "constructed" or "decreed" or anything of the kind. Hence: "what the heavens approve of what is pious", which is the first option that Socrates proffers Ethryphro.
2. Ethics is an externalisation of what is actually and objectively beneficial to those moral agents to which it applies. It flows from and is determined by the nature of those moral agents. It is entirely intrinsic to their nature. Hence an understanding of their nature will give rise to a codification of "the Natural Law" by which they ought to operate if they are to "live long and prosper".
3. The basis of all this is the concept of harmony, cooperation and friendship, both in society and in the soul. The first is social justice, the second is personal justice - or holiness. Both are species of health: the first social and the second psychological and/or physiological. See Plato's "Republic" for a full exposition of this.
4. One of the fundamental characteristics of God is Justice - interior harmony. The fact of God's Immortality and Eternal Robustness implies that God is entirely harmonious and devoid of interior conflict. Hence at this most abstract level the Divine Nature is identical with "The Natural Law" in as far as the Divine Nature generates the Natural Law as a corollary of its self. The Natural Law is an image of the original that is Justice.
5. So far as the details of the Natural Law are concerned, these result from the interplay of the Idea of "Justice" with the particularities of the make-up or constitution or nature of the moral agent to which it is applied. Given that God has created certain kinds of moral agent, with particular characteristics (for whatever reason) then to this extent the Natural Law is "positive" and "decreed" - but only indirectly, in as far as it is true that the details of constitution of the moral agents are "positive" and "decreed" rather than of necessity. Hence: "what is pious is what the heavens approve of", which is the second option that Socrates proffers Ethryphro.