Are two doctrines that I had mistakenly conflated with each other in some of my past posts mentioning Divine Impassability on this blog. But they are related.
Divine Impassibility is the position that God did not suffer when Jesus was on Th Cross, it doesn't deny the Divinity of Christ, but holds that it was only in His Humanity that He Suffered. Divine Immutability is the position that God doesn't change. They tend to go together because Suffering is often both the cause and effect of some kind of Change.
The three way dispute between Chalcedonian, Nestorian and Miaphysite Christologies from the 5th and 6th Centuries is arguably pure semantics since all three were/are Nicene Trinitarians who view Christ as both Fully Divine and Fully Human. The Nestorians held that Christ has two Natures, Divine and Human, that are not in any way mixed. The Miaphysite position is that Christ has One Nature that is both Divine and Human. The Chalcedonian position is that Christ had Two Natures, Divine and Human, that are mixed in the Incarnation. The Bible doesn't directly address any of that, but my understanding of the Biblical Metanarrative leads me to favoring the Chalcedonian position, even if there are some details of the Chalcedonian Confession I don't like.
Thing is what makes these disputes a little less semantical are the other issues tied into them. My greatest affinity with Nestorianism is that I don't like calling Mary Theotokos. However since the technical accuracy of the term is not my issue with it, it's really irrelevant to the actual dispute Nestorius, Cyril and others were having 15 centuries ago.
While Divine Impassability is affirmed by theologians in all three camps, it was the Nestorians for whom it was the core of their position, and they alone who accused both other camps of rejecting Divine Impassability whether they would have self identified as doing so or not. That is why in-spite of my respect for the Ancient Church of the East and how much I prefer the Antiochene School's approach to Scripture over the Alexandrian, I have to reject Nestorian Christology.
Thing is the Nestorians were not wrong to suggest that it's rather illogical to claim Divine Impassability if you believe the Divine and Human Natures were fully United in the Incarnation. Cyril of Alexandria's attempts to justify himself on this involved a lot of Platonist Philosophical nonsense. And that is why I unapologetically reject Divine Impassability.
But I still oppose misrepresenting Nestorius or the Ancient Church of The East, they did and still do believe Christ was one Person/Personality. But the Miaphysites also get misrepresented, they were NOT Monophysites.
The Fifth Ecumenical Council affirmed the Theopaschite formula in it's 10th Canon. And yet Impassability has still been affirmed by theologians belonging to Churches that nominally uphold that Council, thanks to Augustine's influence in the West and Cyril's in the East, so that canon gets ignored. When the Fifth Council is brought up today it's only to debate what/who it did or did not condemn, never what it affirmed. But getting the Theopaschite Formula affirmed was the whole point of the Council at the time, Justinian thought that would be the key to mending the Chalcedonian schism.
The fact that I agree with Justinian on the Theopaschite formula doesn't change that I despise him as a Ruler. His obsession with trying to force everyone to agree only made them dig their heels in deeper.
Another issue related to the Divine Impassability v Theopaschite debate is Patripassianism, did The Father also suffer? I would argue He Suffered in the way any Father watching His Son Suffer would Suffer, but that is distinct from feeling the Physical pain.
Augustine of Hippo used to be a Manichean Gnostic, and the whole reason he once held a Gnostic attitude towards the God of the Old Testament was because he was uncomfortable with the idea of God being so Emotional. It was Ambrose telling he can just allegorize away all of those verses that finally enabled Augustine to abandon Gnosticism and become "Orthodox". To me it is Augustine being someone who doesn't want an Emotional God that is the source of everything wrong with this Theology.
While strictly speaking the word Impassibility refers to is Suffering, to some this doctrine refers to God not feeling Pleasure as well. To me this rejecting of God being an Emotional being at all is pure Platonic/Pythagorean heresy and utterly in conflict with The Hebrew Bible and The New Testament which teaches that God Is Love as the experience of Love tends to involve both Pleasure and Pain.
On the subject of Divine Immutability, it depends what you mean by it. Malachi 3:6 is what most gets abused here as people keep quoting it while ignoring it's context. That God keeps His Promises doesn't change, that He Is Love won't change, therefore He will NOT allow His People to be Consumed. That Core aspect of Who God Is does not change. It's the same with Hebrews 13:8 "Jesus Christ is the same Yesterday, Today and Forever" the context is about Grace and Jesus being a Sacrifice offered for us, it's about His essential character not some absolute declaration that nothing can ever change, as Romans 8:35 and it's context make clear.
But The Bible also refers to God Repenting (See Exodus 32:14 and Numbers 14:12-20; Jonah 3:10; Amos 7:3-9; Jeremiah 26:3), repent means to change one's mind. And I feel the whole point of the Incarnation is that Humanity and Divinity are both permanently changed by being United in Christ. The Hyper Immutability that is favored by Nestorius, Cyril and Augustine is again a heresy based on the Greek and Roman Churches' infatuation with Platonic and Pythagorean theology, not Scripture.
Divine Immutability doesn't begin with Plato or Pythagoras however but with Xenophanes.
There is also the matter of one of the most vital passages to defining God in all of scripture. The famous "I Am that I am" statement, many scholars have argued a more accurate translation would be "I Am who I Am Becoming" or "I Will Be whom I Will Be", meanings that imply change even if in a paradoxical way due to God's knowing the future. I personally have grown to like "I Am whom I Will Be", "Watashi wa watashi ga dare ni naru ka".
Update September 2022: I bought Robert C. Gregg and Dennis E. Groh's Early Arianism - a view of salvation for the purpose of research on the Arian controversy I'm doing for the sake of a possible future post. But two things I didn't expect to learn were. 1. Arius had a fixation on Divine Impassability similar to the future Nestorians. 2. The Arians used Divine Immutability against the Nicenes by proving the changeability of The Son. And this was kind of their greatest strength because Athanasius was unwilling to abandon Divine Immutability.
The Changeability the Arians the argued for The Son was for Improvability, which you may at first think doesn't correlate to the Changeability I am here arguing for The Godhead, but from a certain point of view it is. God incarnating and becoming fully Human made Him a better God. Hebrews stresses how Jesus faced all the Temptations normal humans face yet never sinned. Not sinning is easy when you aren't even tempted, it is facing Temptation and beating it that is a true accomplishment.