He Is One and the Same: The Simplicity and Immutability of God

Introduction

Only the one and unchanging God can truly be the light and hope of the world, as the Scriptures declare He is. This paper will examine those specific attributes of God; namely simplicity and immutability. The former says that God is whole, not composed of parts, and indivisible in the most absolute sense while the latter says that God is without change and cannot be added to or subtracted from. These attributes are inseparably related to one another in the way that one necessitates the other and how they work together to hold up the doctrine of God as the Perfect Being and the doctrine of the Trinity.

Defining Simplicity and Immutability

It is appropriate to first define the attributes that are in discussion. Beginning with the attribute of divine simplicity, in its purest form it means, “God is one; he is singular perfection.”Footnote 1 This is not just one in its numeric sense, but more so in the sense of wholeness as seen in Deuteronomy 6:4, “Hear, O Israel: The LORD our God, the LORD is one.”2 

Many classical theologians defined this attribute in the negative sense, negative meaning through saying what God is not. Anselm of Canterbury says, “whatever is made up of parts is not absolutely one” but of God says, “Indeed You are unity itself not divisible by any mind.”3 For Saint Thomas Aquinas, simplicity relates to composition, in the case of God the lack thereof. God does not have a body and is the first and essential being in which all of creation, which is composed, participates in for their form and goodness. Because of this, he declares, “it is impossible that God should be composed of matter and form.”4 Similarly, second century bishop Irenaeus of Lyons saw humans as “compound by nature, [consisting] of a body and soul” in contrast to God who is, “is a simple, uncompounded Being, without diverse members”.5 Taking all of this into consideration, simplicity may be defined either in the negative; God is uncompounded and not composed of parts, and in the positive; God is one.

Closely related to simplicity is the attribute/doctrine of divine immutability, which relates to change in God, or rather the lack of change. Renowned Dutch theologian Herman Bavinck presents immutability as, “While everything changes, God is and remains the same.”6 The inspiration of this definition is Psalm 102:25-27,

“Of old you laid the foundations of the earth, and the heavens are the work of your hands. They will perish, but you will remain; they will all wear out like a garment. You will change them like a robe, and they will pass away, but you are the same, and your years have no end.”

British theologian Stephen Charnock uses these same verses, claiming that “you are the same”, “not only assert[s] the eternal duration of God, but his immutability in that duration.”7

Immutability does not only mean that God remains the same, but also that nothing can be added to Him or subtracted from Him. For Charnock, that meant that God “wants nothing [and] loses nothing.”8 Others describe this in terms of potential. Matthew Barrett says, “Potential, by definition, assumes someone has yet to reach a state of fulfillment.”9 To avoid charging God, who is perfection in and of Himself, with having potential, Aquinas states, “God is pure act, without any potentiality.”10 Being “pure act”, God has no need to add anything to Himself or change anything about His being. As Barrett puts it, “nothing need be activated in God, as if he were in need of becoming something more than he already is.”11 Rather, God is the “Perfect Being”12 as Katherin Rogers argues. The Perfect Being has no need of any additions as He is perfection, and cannot have anything taken away from Him as this would cause Him to be less than perfect. The Perfect Being, God, must then be immutable.

Relating Simplicity with Immutability

These divine attributes of simplicity and immutability are inseparably connected. It is often the case that where one is found within theology, the other is close by. It can be difficult to even talk about one without bringing up the other. This section of the paper will explore this relationship in three specific ways, the first being in how one attribute necessitates the other; a simple God cannot be a changing God, a God that can change is inherently composed of parts and therefore not simple.

Simplicity necessitates immutability specifically in the way it holds all of God’s attributes together. Barrett uses the analogy of a pie to describe how not to think about the attributes of God. Nobody bakes a pie and then decides to eat it as a whole, especially if it is being shared. Rather, the pie is (hopefully) evenly cut into pieces that make up the whole. “Unfortunately, this is how many Christians talk about God today, as if love, holiness, and omnipotence were all different parts of God, God being evenly divided among his various attributes.”13 Simplicity, however, guards against this. Through simplicity God is kept as whole, one, and not composed of parts that are able to be divided in the first place. 

If this were not the case, it is entirely possible that one attribute of God could be elevated above another, forcing God to be more loving than just in one instance and more holy than merciful in the next. Naturally, then, this would force God to change; adapting and reacting to different situations as they come. This would be disastrous for Christians who depend on God to be their steadfast rock and refuge. How could they depend on this divided, mutable God? Fortunately, God is simple, and as Augustine of Hippo says, “nothing simple is changeable.”14 “Incorporeal and immutable, God is identical with his perfections. This is what it means for God to be one.”15 So if God is simple, He must also be immutable.

The reverse is true as well, if God is immutable then He must be simple. Charnock implies how immutability necessitates simplicity by saying, “Immutability is a glory belonging to all the attributes of God” and “is the center wherein they all unite.”16 So important is this attribute of immutability that without it “the rest would come undone.”17 God would no longer be the Perfect Being, as His love, power, or wisdom could diminish at any point in time. All of these attributes rely on immutability to be perfect within God, otherwise it could not be said, “Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!” (Romans 11:33) If His wisdom and knowledge could diminish, then perhaps one day His judgment and ways could be searchable and comprehensible. This would mean the Scriptures bear false witness about God,  and Christianity would lose its foundation. Immutability is the “enamel”18 that keeps it all from falling apart.

Because of this, it can be said that “It is because God does not change that he remains simple.”19 Remember, simplicity means that God is not composed of parts. Any change within God, whether introduced through addition or subtraction or if God somehow changed Himself, would inherently mean that He is now composed of different parts. His parts, then, would have to interact with each other, leaving believers with the question, “which attribute of God will win out in this scenario?” This turns God into nothing greater than the pantheon of Greek gods that are sometimes god-like, sometimes human, and capable of acting in sin. But the apostle Paul makes it clear that this is not who God is, proclaiming in Athens, “The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man, nor is he served by human hands, as though he needed anything, since he himself gives to all mankind life and breath and everything” (Acts 17:24). God needs nothing, for He is life in and of Himself, the source of life for all, and is perfectly whole. This is why “Immutability is key to preserving God’s simplicity.”20

Another way simplicity and immutability are related is in how they work together to hold up the doctrine of God as the Perfect Being. In his Proslogion, Anselm argues that God is “something than which nothing greater can be thought.”21 The gist of this argument is the greatest thing that can possibly be thought of; in very being, power, knowledge, etc., must exist in reality to really be the greatest being. Rogers calls his argument the starting point of “perfect being theology.”22 What does it mean for God to be the Perfect Being? Simplicity and immutability are two key components in answering this question.

Throughout the Proslogion Anselm recognizes and describes the many attributes of God that make Him this Perfect Being. He eventually comes to this question, “How then, Lord, are You all these things? Are they parts of You, or rather, is each one of these wholly what You are?”23 If something is made up of parts, he says, “it can be broken up either actually or by the mind”.24 Something that can be broken cannot possibly be perfect. Even the potential to be somehow broken up must be “foreign”25 to the Perfect God. 

In this argument Anselm employs both simplicity and immutability. If God is to be the Perfect Being then He cannot be made up of parts, “but all [attributes of God] are one and each of them is wholly what You are and what all others are.”26 This is simplicity. For this to be true, however, there must be no potential for these attributes to separate from one another. Remember, “Potential would mean he needs to grow in his perfection”27, but the Perfect Being is perfection, not needing to achieve it. There was never a time when He had potential, when He lacked perfection but then achieved it. No, God as the Perfect Being must be perfection itself in all of eternity. Having no potential to change, then, means that the Perfect Being is immutable. For God to be God, who is perfection, He must be simple, not composed of parts, and immutable, never changing or having the potential to change or have different parts.

A final, very important, way simplicity and immutability are related is in how they work together to uphold the doctrine of the Trinity. Many, if not all, of the Church Fathers embroiled in the fourth century Trinitarian Controversy with the Arians appealed to these attributes to show how God can be one God in three Persons. 

Much of this controversy surrounded the “generation” of the Son, meaning how it is that the Son is begotten from the Father. Interestingly, both sides accused the other of distorting the simplicity and immutability of God. In his letter to Alexander of Alexandria, Arius claimed that those who believe the Son’s generation from the Father, “signify that he is a part of him and an emanation, the Father will be according to them compounded, divided, mutable, and a body”28. His argument was that for the Son to be begotten from the Father’s essence, or being, God would have to have something taken from Him, thereby being compounded and mutable. Instead, Arius argued, the Son was created by the Father and unlike Him in essence.

This, however, is a misunderstanding of those who contend the Son comes from the Father’s essence eternally, known as eternal generation. Contrarily, proponents of eternal generation, such as Athanasius of Alexandria, saw this as the only way to preserve the simplicity and immutability of God. Athanasius recognized the difference between the way humans generate and the way a simple, immutable God generates,

“For the offspring of men are portions of their fathers, since the very nature of bodies is not uncompounded, but in a state of flux, and composed of parts; and men lose their substance in begetting, and again they gain substance from the accession of food. And on this account men in their time become fathers of many children; but God, being without parts, is Father of the Son without partition or passion; for there is neither effluence of the Immaterial, nor influx from without, as among men; and being uncompounded in nature, He is Father of One Only Son.”29

It is precisely because God is simple and uncompounded that eternal generation does not divide His essence. Instead, “if the Father is immutable and he remains what he is, the image necessarily remains what it is and will not be mutated.”30 So the Trinity, through eternal generation, is held up by the simple, immutable nature of God.

Inseparable Operations is another way the Church Fathers held up the Trinity through simplicity and immutability. This doctrine says that whenever God works or acts upon the world, all three Persons of the Trinity are working inseparably and therefore the One, simple God is at work. Augustine uses fewer words, defining it as, “the Trinity works indivisibly in everything that God works.”31 Gregory of Nyssa says that, “No activity is divided to the hypostases (Persons)”32 but that all are, “one and not three, kept straight by the holy Trinity.”33

In his work, On the Holy Spirit, Basil of Caesarea appeals to inseparable operations to prove that the Holy Spirit is co-equal with the Father and the Son against the “Spirit-Fighters” who ranked the Spirit below the Father and the Son in terms of glory. Showing “the unity and indivisibility in every work of the Holy Spirit from the Father and the Son”34 Basil illustrates how the Holy Spirit, along with the Father and the Son, is involved in the works of creation, the Incarnation (the Son as fully God, fully man), the resurrection of the dead, the beginning of the Church, and the judgment to come at the end of days. This argument of inseparable operations serves his purpose because, “glory is nothing other than the recounting of the wonders that belong to him.”35 If the Spirit is indivisible from the Father and the Son in these works, then He must be indivisible in glory as well.

This argument, and the concept of inseparable operations itself, is built on the foundation laid by simplicity and immutability. Only a simple Trinity, who is “one in essence, will and power”36 may also work “inseparably in creation and salvation.”37 As Barrett says, “indivisible in essence, indivisible in operation”38. Only an immutable Trinity may remain one while working as three Persons. This guards against the heresy of modalism which says, “The one God is Father, and then he decides to become Son, and at another time Holy Spirit.”39 It is no stretch of the imagination, then, to argue that without simplicity and immutability there is no valid argument for the doctrine of the Trinity.

Engaging Objections

There are, however, some modern theologians that reject these doctrines of simplicity and immutability, raising some objections that are important to address. This section will engage with R.T. Mullins and Jürgen Moltmann specifically, who argue that these attributes are incompatible with the Incarnation and that holding these attributes up make God impersonal, respectively.

In his 2013 article, “Simply Impossible: A Case Against Divine Simplicity” for the Journal of Reformed Theology, R.T. Mullins sets out to discredit the doctrine of divine simplicity through pointing out several apparent “inconsistencies” between the doctrine and Scripture. With limited space, this paper will only engage with his assertion that “divine simplicity [is] in direct conflict with any adequate Christology”40 because of the Incarnation. His argument for this is that because of the “communicatio idiomatum—the communication of the properties onto the Word”41, the Incarnation is incompatible with simplicity or immutability. The fact that “In the incarnation the Word takes on a whole host of properties”42 means for Mullins that God must have changed in this event, meaning He must also be mutable and composed of parts.

The fatal flaw of Mullins’ argument is that he conflates the immanent Trinity with the economic Trinity; immanent meaning “who the triune God is in Himself” and economic, “how the triune God acts in relation to creation and in the economy of salvation”, according to Barrett.43 While God does reveal who He is in Himself through His works in the economy, such as the Incarnation, they do not “constitute”44 His nature. By mapping the human properties of the Incarnation (being mutable and compounded) onto the nature of God, Mullins is guilty of this conflation. 

Contrary to what Mullins believes, the whole of the Bible actually points to a simple, immutable Trinity. Previously referenced passages Deut. 6:4 and Ps. 102:25-27, along with many more, have clearly shown this. If these attributes can be rightly said of the Father, they may be rightly said of the Son as well. In light of Jesus’ words, “Whoever has seen me has seen the Father” (John 14:9), Athanasius makes the case that, “Since the Father’s substance is immutable, his peculiar offspring from him would be immutable.”45 Barrett agrees, saying, “If he [the Son] is from the Father’s nature, a nature that is not only simple and eternal but immutable, then no change can occur in generation.”46

All this in consideration, it cannot be said that the Incarnation is incompatible with divine simplicity and immutability. The Chalcedonian Definition sums it up well: “at no point was the difference between natures [of the Son; human and divine] taken away through the union, but rather the property of both natures is preserved and comes together in a single person and a single subsistent being”.47

Twentieth century theologian Jürgen Moltmann lobs a different objection towards the simple, immutable God in his work, Crucified God. In this book, he rejects the impassibility of God; the attribute that according to Thomas Weinandy says, “he cannot experience emotional changes of state due to his relationship to and interaction with human beings and the created order.”48 His main objection with impassibility is that it prevents God from being capable of suffering. For Moltmann, “Were God incapable of suffering in any respect, and therefore in an absolute sense, then he would also be incapable of love.”49 Barrett explains that this attack on impassibility is also an attack on the rest of God’s attributes, saying, “Moltmann directly confronts…[those] who would claim God is “absolute” or “pure act,” affirming not only impassibility but with it divine immutability, aseity, omnipotence, and infinitude as key to a perfect being. Such a view makes God indifferent, apathetic, and cold.”50

What Moltmann fails to recognize, however, is that “impassibility actually protects other attributes like love, because it guarantees that his love will not change or fluctuate.”51 By rejecting God’s impassibility, he creates a God who can be changed by, or at least can will Himself to be changed by, His creation. As has been outlined previously, if God can change then it also inherently means He is made up of parts, no longer being simple. If all of this were true about God, what would there be to guarantee that suffering in God produced by His creation would result in love? It could be equally possible that this kind of suffering could produce resentment in Him, and as a result His creation would be destroyed by His wrath rather than redeemed by His love. This is not the God of the Bible.

In contrast to Moltmann, Barrett argues, “God is compassionate, loving, merciful, and caring because, and only because, he is impassible.”52 The same is true because He is immutable and simple. It is only a simple and unchanging God that can truly be the light and hope of the world.

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______. Simply Trinity: The Unmanipulated Father, Son, and Spirit. Grand Rapids, MI: Baker Books, 2021.

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Moltmann, Jürgen. The Crucified God: The Cross of Christ as the Foundation and Criticism of Christian Theology. San Francisco, CA: Harper San Francisco, 1991.

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