Divine immutability; it is sometimes thought of as a purely philosophical lens imposed upon the God revealed in Jesus Christ and Holy Scripture (think of people like Pinnock, Harnack, et al.). For some it has functioned very much so in this way. For others, like Richard Muller, he believes that the whence of immutability, from its classically Hellenic sources, has been transmogrophied by the Christian witness such that its good kernel has been retained while the flowery husk has been discarded. But what is a basic working definition of Divine immutability? The Stanford Encyclopedia of Philosophy puts it this way:
For one thing, the Scriptural witness is not really so clearly on the side of divine real intrinsic change. Much that Scripture says of God is clearly metaphor. And it is not hard to show that Old Testament texts which ascribe change to God could be speaking metaphorically. As I note later, one can parse even the Incarnation in ways which avoid divine real or intrinsic change. Standard Western theism clearly excludes many sorts of change in God. Western theists deny that God can begin or cease to be. If God cannot, He is immutable with respect to existence. Nothing can gain or lose an essential property, for nothing can fail to have such a property. For Western theists, God is by nature a spirit, without body. If he is, God cannot change physically — he is physically immutable. So the Western God could at most change mentally- in knowledge, will, or affect. Further, Scripture amply supports the claim that God is perfect in knowledge, will, and affect. This perfection seems to rule out many sorts of mental change.
The primary thing that stands out is ‘change,’ or lack thereof. Another attending issue is that of ‘movement,’ which might imply change; i.e. if God is made to respond by something that is a predicate of his life (e.g. something that is contingent upon him rather than vice versa). Richard Muller cites Lutheran theologian Johannes Quenstedt, and provides further theological elaboration thereby:
We can see the attempt to recuperate immutability, or to appropriate it in such a way that it just is corollary with the prima facie teaching of Holy Writ. Interestingly, at one level, Muller himself places Barth on the side of the immutabilitists before he launches into critique of Barth. Muller writes,
While this is interesting, and to the point, I think I’d rather hear from a Barth scholar, like Paul Molnar, as he details just exactly upon what basis Barth thinks God’s immutability from. It indeed coheres with the basic contours of the intentions of classic immutability (that God cannot be moved by something external to him), but then reifies in such a way that the affections of God are not just understood as metaphors or anthropopathisms, but instead as reflective of who God actually is in himself (in se). Here Molnar is responding to the ‘Barth Wars,’ indeed he is contributing to it contra Bruce McCormack’s et al. idea that God’s electing work precedes who God is as triune thus allowing creation itself to determine who God chooses to be for us in the incarnation (Deus incarnandus). This is the context from which I take this quote from Molnar (for full disclosure). For our purposes what shouldn’t be lost is how Barth’s conception of immutability and mutability (or not) function in his theology; I would suggest this is the better way forward. While retaining the important node that God does not change, what is forwarded within that reality is that God does indeed genuinely love and feel; because he wants to; because this is how we know him to be from his Self-revelation in the Son (Deus incarnatus). Molnar writes:
Because it has been said that Barth’s view of God’s freedom changed after CD II/2, it is imperative to note here that Barth wanted to break the spell of an idea of God that was either mutable or immutable in the sense that God could not humble himself in Jesus Christ but that in the “supreme exercise” of his essence he could, as the immutable (constant) God, accomplish reconciliation for us. Nonetheless, Barth insists even here, “It is not that it is part of His divine essence, and therefore necessary, to become and be the God of man, Himself man. That He wills to be and becomes and is this God, and as such man, takes place in His freedom. It is His own decree and act. Nor is there anything in the essence of man to make necessary this divine decree or act” (IV/2, p. 85). What, then, is the divine essence that remains unchanged in all of this, Barth asks? He says, “It is the free love, the omnipotent mercy, the holy patience of the Father, Son and Holy Spirit. And it is the God of this divine essence who has and maintains the initiative in this event. He is not, therefore, subject to any higher force when He gives Himself up to the lowliness of the human being of the Son of God” (IV/2, p. 86).
We see, according to Molnar, how Barth negotiates his way through the dilemma that has been set up between God’s so called immutability and mutability. For Barth this dilemma really is no dilemma, instead it represents an occasion to creatively construct a way through this apparent morass that recognizes the biblical significance that God does indeed not ‘change,’ but then pushes forward through the usually Ramist ways of negotiating with this, and instead attempts to think these issues through a personalist lens that starts with the hypostasis of the eternal Word of God, Jesus Christ. What bubbles up from this exercise is that God’s triune love grounds the way Barth thinks about ‘how’ God moves; he concludes that God’s movement is Self-determined and located in Divine freedom to be who graciously chooses to be for the other; all implicates of who God is eternally as Father, Son, and Holy Spirit.
 Paul D. Molnar, Faith, Freedom and the Spirit: The Economic Trinity in Barth, Torrance and Contemporary Theology (Downers Grove, Illinois: IVP Academic, 2015), 273 n. 14.
*The Muller quotes come from this essay.