Al-awfaq wa-l-aṣlaḥ here draws attention to proportion, wisdom and suitability in the world's ordering. The reasoning is not merely that things exist, but that particular ordered relations obtain.
Coordination among elements provides an example of a determinate arrangement among possible alternatives. The question is why such specification is attributed to power and will.
This is not simply the Muʿtazilī doctrine of the obligation to do what is best. Reasoning from wise order and asserting that God is obligated by an external standard are distinct propositions.