According to Trinitarian theology as held by the Catholic and Orthodox Churches, God is 3 persons/hypostasis in 1 essence/nature/substance and one attribute of God is his immutability (c.f. Summa Theologica Ia Q9 A1) yet it is also the case that Christ is both true God and true man. This latter doctrine is called the hypostatic union referring to the two natures (divine and human) present in one person (hypostasis).

How are these doctrines both held as true?

  • This answer to another question also answers this question.
    – Nigel J
    Commented Aug 9, 2023 at 8:42
  • @NigelJ No, it doesn't. That question doesn't mention immutability at all. It asserts correctly that person and nature are different but doesn't address how the 2nd nature which begins to exist in time is not a change to the person that affects the claim of immutability of God
    – eques
    Commented Aug 9, 2023 at 12:44
  • Your comment proves the point. You say 'a change to the person'. It is not. It is an addition of a nature. There is no 'change to the person' - which is exactly the point of the answer I linked to. Quod erat demonstrandum.
    – Nigel J
    Commented Aug 10, 2023 at 8:40
  • @NigelJ No, I said "doesn't address how... is not a change to the person"; The linked answer does not mention change nor immutability and hence cannot be an answer against this question on its own.
    – eques
    Commented Aug 10, 2023 at 10:14

1 Answer 1


My answer is based on how Fr. Thomas Joseph White explained the following in two Church Grammar podcast episodes: Tough Christology Questions and Tough Trinity Questions.

Below is a very rudimentary explanation; I highly encourage you to listen to the entirety of both episodes.

  1. the 3 levels of presence of God in the created realm, that from our point of view is God's omnipresence
    • in all created beings (giving it individual nature as well as sustains its existence)
    • presence of grace (giving us a share of Trinitarian life and a fellowship with Him as adopted son/daughter through Christ)
    • unique incarnation in the historical human nature of God: Jesus Christ
  2. how the Incarnation is willed out of eternity by all 3 Trinitarian persons in that only the 2nd person obtains a body at a particular time in history as a temporal effect, not as essential change in God's own being (i.e. God's Trinitarian nature does not improve or being more fulfilled with Jesus's bodily experience in history). In other words, Jesus's divine nature while being incarnated does not change, and what we see Jesus was doing is the 3rd mode of presence.
  • I think point number 2 needs elaboration, specifically how what seems to amount to a change in the person (the temporal effect of the human nature)
    – eques
    Commented Aug 9, 2023 at 0:04
  • @eques Fr. Thomas White in his Trinity episode discussed at length the modern theology's tendency of not only reducing Jesus's divinity (so Jesus can be "more human") but also how since Hegel, there is a great shift of how theologians try to understand the the inner life of the bodi-less Trinitarian God as undergoing development in history to make it more palatable to modern sensibilities (minutes 10:30 to 2:00), exemplified by Karl Rahner's Axiom "The economic Trinity is the immanent Trinity, and vice versa", possibly contributing to our being predisposed to reject immutability. Commented Aug 9, 2023 at 0:18
  • Fr. Thomas White may cover that, but my point is about what is actually expressed in the answer. It's not only a body but a soul (i.e. a complete human nature) that is attained by the 2nd person in time and yet God is immutable. So what is the meaningful distinction to make around person, nature, essence, etc to describe what is immutable and not and what undergoes change or how?
    – eques
    Commented Aug 9, 2023 at 12:58
  • @eques I will need more time to improve the answer, but in the meantime this comment space can give me the points I need to address. In the Trinitarian Chalcedonian definition Jesus's human nature has a 100% human soul like us (not just body) that without confusion and without separation "the difference of the Natures being in no way removed because of the Union, but rather the properties of each Nature being preserved and (both) concurring into One Person and One Hypostasis". Now Aquinas and Fr. Thomas White, a Thomist, tried to help us process that definition in philosophical terms ... Commented Aug 10, 2023 at 15:25
  • ... and being downstream from them both, I tried to faithfully summarize how they do it, tailoring to your question. To answer your comment, yes, there are 2 souls here (if we can call God a "soul"), but more precisely 2 minds and 2 wills (one set divine, another human). And we can conceive that Jesus's human soul DOES undergo change, like all other modes of presence of God in this world. But change in the world is "out of scope" with regards to God's immutability as defined in Question 9, as God is Spirit and Jesus (having a body animated by his human soul) is separate than the Holy Spirit. Commented Aug 10, 2023 at 15:34

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