By Clement Harrold
May 28, 2026
One of the defining attributes of God is that He is immutable, meaning He isn’t subject to change.
We know this through philosophical reasoning because at the foundation of reality there has to be one being who is purely actual without any potency, and we call this being God.
We also know about God’s immutability through the witness of Sacred Scripture:
For I the LORD do not change; therefore you, O sons of Jacob, are not consumed. (Mal 3:6)
Jesus Christ is the same yesterday and today and for ever. (Heb 13:8)
Every good endowment and every perfect gift is from above, coming down from the Father of lights with whom there is no variation or shadow due to change. (Jas 1:17)
The doctrine of divine immutability is further affirmed in the Church’s liturgical life, such as in the great Hymn of the Incarnation chanted after the Second Antiphon in the Divine Liturgy of St. John Chrysostom:
O only begotten Son and Word of God, who being immortal, deigned for our salvation to become incarnate of the Holy Theotokos and ever-Virgin Mary, and became man without change. You were also crucified, O Christ our God, and by death have trampled death, being One of the Holy Trinity, glorified with the Father and the Holy Spirit, save us.
All of this raises a difficulty for the Christian. If God cannot change, then how could the Second Person of the Trinity become a human being at the moment of the Incarnation? And how could that human being then do things such as growing, walking, suffering, and dying? These are clearly changes, and so it seems that God isn’t immutable after all.
Over the centuries Catholic thinkers have tackled this issue in different ways.
The philosopher Michael Gorman, who follows the approach of St. Thomas Aquinas, argues that when the Second Person of the Trinity becomes a human being, He thereby becomes mutable (in a certain sense) insofar as He now possesses a human nature, and this human nature is subject to change.
Here we need to clarify two points.
First, the Father and the Holy Spirit remain immutable by virtue of their divinity and because, unlike the Son, they do not assume a human nature.
Second, the human nature assumed by the Son neither changes nor diminishes His divine nature. In the hypostatic union, the divine and human natures subsist together in the one divine Person of the Son without confusion, mixture, division, or separation.
Gorman also points us to Aquinas’s teaching that the Son, like the Father and the Spirit, is perfectly simple in Himself. (Here we are using “simple” in its metaphysical sense, meaning not composed of parts.) Unlike the Father and the Spirit, however, the Son subsists in two different natures, and in this respect He is a composite (i.e. non-simple) Person.
Aquinas explains the distinction:
There are two ways in which to think of the person or hypostasis in Christ: In one way, as it exists in its own right. And on this score it is altogether simple, just as the nature of the Word is simple. In the second way, according to its character as a person or hypostasis, which involves its subsisting in some nature. And on this score, the person in Christ subsists in two natures. Hence, even though in this case there is one thing that subsists, there is one and another notion of subsisting. And in this sense the person is called ‘composite’, insofar as one thing subsists in two things. (Summa Theologiae, III.2.4, trans. Alfred J. Freddoso)
We see, then, that the Son is one divine Person with two distinct natures.
Moreover, it’s important to recognize that the Son is subject to change through one (and only one) of these natures: In His human nature, the Son truly is capable of growing, moving, learning, suffering, and dying. However, these changes do not in any way affect His immutable divine nature.
This still leaves us with a major unanswered question; namely, how was the Son able to become human in the first place?
Aquinas points out that the creation of the Son’s human nature raises similar difficulties to all the other acts of creation: these acts seem, at first glance, to contradict God’s immutability. Doesn’t God undergo a change from non-Creator to Creator? And doesn’t the Son undergo a change from non-human to human?
These are deep mysteries, and so our answers will necessarily be imperfect.
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The pertinent question concerns the Son’s relationship to His human nature (in the case of the Incarnation) or God’s relationship to the material world (in the case of creation). Here Aquinas distinguishes between real relationships and mixed relationships.
A real relation involves a quality that two beings share in common. Thomas and Jane both possess physical mass, and Thomas really is taller than Jane, while Jane really is shorter than Thomas.
A mixed relation, by contrast, is one-sided. When Thomas thinks about Jane, something changes in him but not in her. He is really related to Jane in this moment, but Jane is only logically related to him.
As Aidan Kimel explains, their relationship is thus asymmetrical, or mixed. Thomas has thought about Jane, and Jane has been thought about by Thomas, but this comes about only because of something in Thomas, and not because of anything in Jane.
Now for Aquinas, the Son’s relationship to His human nature (as well as God’s relationship to creation) is a mixed relation. Michael Gorman explains:
There is no relational accident joining the Son to the assumed human nature, but there is a relational accident in the assumed human nature joining it to the Son. On this way of thinking, although there is a relation between the Son and the assumed nature, the establishing of this relation does not involve any actualization of a potency in the Son, and therefore it is not a mutation of the Son, and therefore it does not violate divine immutability. (“Two Problems,” 906)
Gorman then clarifies an important point:
It is important to realize that the relation between an ordinary creature and God is not entirely the same as the relation between the assumed human nature and the Son. God creates a cow, and the cow is related to God by a mixed relation, but God does not therefore become bovine. When a bovine nature comes to be, it comes to make some substance bovine, but its coming to be is concomitant with the coming to be of the substance that makes it bovine, a substance distinct from any divine person. The Incarnation has to be different from this. In the Incarnation, a human nature comes to be, but instead of giving rise to some non-divine human person, it makes a divine person human. (“Two Problems,” 907)
From here, Gorman proceeds to explain how, as creatures, we are by definition limited.
I am a human being, and to be human is to lack things like wings, gills, and scales. God, by contrast, is unlimited. Yet what He chooses to do in the Incarnation is to adopt a limited human nature.
Gorman gives the analogy of keys for a vast building.
Human beings are limited creatures who only possess what are known as “change keys,” i.e., keys that only open the door to one particular room.
God, on the other hand, is the unlimited Creator who possesses the master key that opens all the doors in the building. In the Incarnation, however, God voluntarily comes to possess one of the change keys:
He still has a master key and can still open any door, but he also has a particular change key with which, if he so chooses, he can open one particular door. The building administrator who had a change key to my office could choose to enter my office with that change key rather than with the master key (we can imagine that he might do so in order to show solidarity with me, or out of humility). . . . One important difference between this case and the Incarnation is that, in the key example, the administrator who humbly uses a change key must use it instead of the master key. In the Incarnation, by contrast, Christ always acts by his divine power, but sometimes he acts by that power alone, and at other times he acts by that power and also by his human power, in such a way that the human power is an instrument of the divine. (“Two Problems,” 910)
The Incarnation therefore does not imply a change in the divine nature or a movement from potency to actuality in God. Rather, the eternal Son assumes a human nature into personal union with Himself while remaining fully immutable in His divinity.
In this way classical Christian theology maintains both the reality of Christ’s human life and the unchanging perfection of God.
Become a MemberFurther Reading
Michael Gorman, “Christ as Composite according to Aquinas” (Traditio, 2000)
Michael Gorman, “Two Problems concerning Divine Immutability and the Incarnation” (Nova et vetera, 2018)
Timothy Pawl, “Conciliar Christology and the Consistency of Divine Immutability with a Mutable, Incarnate God” (Nova et vetera, 2018)
Fr. Gregory Pine, O.P., “Exploring Divine Simplicity and the Incarnation”
Tim Staples, “If God Became Man, Didn’t God Change?”
Thomas G. Weinandy, O.F.M.Cap., Does God Change? (St. Bede’s Press, 2002)
About Clement Harrold
Clement Harrold earned his master’s degree in theology from the University of Notre Dame in 2024, and his bachelor’s degree in theology, philosophy, and classics from Franciscan University of Steubenville in 2021. He is a columnist for The Catholic Herald, and his writings have appeared in First Things, Word on Fire, Catholic Answers Magazine, Church Life Journal, Our Sunday Visitor Magazine, Crisis Magazine, and the Washington Examiner.
