You cannot go beyond God to find a reason for ethics. If you did so, then you cannot do it without establishing a dual ontology or authority with/over God. God’s sovereignty over you is what makes a command a command, and not something else. God created you, in absolute sovereign power. You are not free from God’s hold on metaphysics and His revealed definitions about mankind, and this is the foundation for ethics. Consider our patriarch King David. Compare his words to Romans chapter 9. David says because God created him, (A sovereign authority over David, which David is not free from) he needs to understand how to obey Him.
Ps 119:73 LEB“Your hands have made me and established me;give me understanding that I may learn your commands.”
Or Paul’s argument:
If the Creator takes me from a neutral clay lump(that is not already bad) and makes me into a wicked pot, and I obviously go along with God’s causality, then why does God find fault with me, even if He commanded me to do good? He finds fault because you did not do what He commanded, regardless of the ontology of it.
Romans 9,“Well then, you might say, “Why does God blame people for not responding? Haven’t they simply done what he makes them do?””
Both affirm God’s commands presuppose the fact God is a sovereign over something, and that this something is not free relative to God. Paul takes it further by saying, even if God causes (on the ultimate level ) you to behave against His commands (like He did with Pharaoh) you are still accountable because God is a sovereign creator over you, and you are not free from Him. As said before, God is the foundation of all theology. The issue is that God will do what He wants. If he decides to hold Pharaoh or a fig tree accountable, then its accountable, regardless of anything else that might be added.