I am sure that this must have been posted before but as a refresher in the context of recent posts it may be helpful.
In refuting Eunomios, who claimed that the essence of God is revealed by created things, St Basil the Great writes that ‘created things manifest wisdom, art and power but not essence’. Thus the divine energy made manifest by created things is both uncreated and yet not God’s essence; and those who like Barlaam and Akindynos say that there is no difference between the divine essence and the divine energy are clearly Eunomians.
St Gregory Palamas Chapter 83: “Topics of Natural and Theological Science” in The Philokalia Vol 4. A few more quotes from the same source relating the distinction of essence and energies to will:
If the divine essence does not in any respect differ from the divine energy, then the act of generation and of procession will in no respect differ from the act of creating[,]… then neither does it differ from the divine will. Thus the Son who is begotten from the Father’s essence, is according to these people also created from the Father’s will[,]… and if the holy fathers testify that God has many energies – for… He has creative providences and goodnesses – then God also has many essences. This is a view that no member of the Christian race has ever uttered or entertained.
If the energies of God do not in any respect differ from the divine essence, then neither will they differ from one another. Therefore, God’s will is in no way different from His foreknowledge, and consequently either God does not foreknow all things – because He does not will all that occurs – or else He wills evil also, since He foreknows all. This means either that He does not foreknow all things which is the same as saying that He is not God, or that He is not good, which is also the same as saying He is not God. Thus God’s foreknowledge does differ from His will, and so both differ from the divine essence.
If the divine energies do not differ form one another, then God’s creative power is not distinct from His foreknowledge. But in that case, since God began to create at a particular moment, He also began to foreknow at a particular moment. Yet if God did not have foreknowledge of all things before the ages how could He be God? If God’s creative energy does not differ in any respect from divine foreknowledge, then created things are concurrent with God’s foreknowledge. Thus because God unoriginately has foreknowledge and what is foreknown is unoriginately foreknown, it follows that God creates unoriginiately, and therefore that created things will have been created unoriginately. But how shall He be God if His creatures are in no way subsequent to Him? If God’s creative energy in no respect differs from His foreknowledge, then the act of creating is not subject to His will, since His foreknowledge is not so subject. In that case God will create, not by an act of volition, but simply because it is His nature to create. But how will he be God if He creates without volition?
As St Gregory demonstrates, one gets into many difficulties holding absolute divine simplicity without distinguishing between essence and energies, or by trying to force the God of Revelation into pagan theistic models and categories, which I believe are insufficient to deal with the Trinity, the Incarnation and creation beginning by God’s volition at a particular moment from non-existence. It follows, in line with St Gregory, that only with the essence/energy distinction can one hope to be speaking of the Biblical God. Also, although not to be taken too far, we can see from our understanding of created energy that the uncreated divine energies tell against a static God but rather tell of a dynamic God. Of course God transcends human/created experience of dynamism and He is not subject to changing His mind nor to passions. These things in Scripture are not pointing to who God is but to our synergy in salvation. It tells of our freedom of will because God is unchanging in willing all men to be saved but yet few are chosen. Our choices bring different consequences, which can be described in human terms of God relenting or getting angry, but one should not ascribe these to God in a human way of changing His mind or becoming passionate.