From Simplicity flows Immutability, which, as it was organized by our AUTHOR, is proven, 1. From Sacred Scripture, among other passages, James 1:17, where to God is denied, not only παραλλαγὴ/ variableness, but even any τροπῆς ἀποσκίασμα, shadow of turning/ change. The very Sun in the eclipse of its Light suffers, if not change, at least shadowing: but not so the Father of Lights, in whom there is not even the slightest appearance of change. For an illustration of this text from James carefully examine BULL’S Harmoniam Apostolicam, second dissertation, chapter XV, § 20, pages 101, 102. 2. From Reason, drawn,
α. From Simplicity, which, since it excludes parts, also does not admit one and another composition of them. No one is at all able to feign a mutable Deity, unless that Deity be at the same time composite, or at least liable to compounding; because whatever is mutable supposes a true distinction among the multiple predicates, and the possible union of the same among themselves, or disunion from each other.
β. From consummate Perfection, which excludes mutability, because,
a. It is Infinite. You may neither add to, nor detract from, God, so as to prevent the like acknowledgement that such riches of Perfections are not in Him, of what greatness belong to the thing that exerts influence over true Infinity, the nature of which rejects all diminution and augmentation.
b. It does not admit mutation either for the better or for the worse. For, if you should say that God by mutation passes into an equal state, you are advancing things truly ridiculous; since a mutation of this sort would obviously be useless. But whether you choose God to be changed for the better, or for the words; both imply Imperfection, past, present, or future.
c. Also, God would be changed either by another, or by Himself: supreme and infinite Perfection admits neither. a. God is not able to be changed by anything that is extrinsic to Himself because of His Aseity and Independence as the first Being. For everything that is changed by another to that extent depends upon the thing changing it as a cause; and so God in such a case would depend upon another more powerful thing as a cause. b. He is not able to be changed by Himself. For, to this, 1. God is not able to be induced to change Himself, because of anything in Himself, since He contains nothing within Himself that is in tension with Himself. Nor because of anything outside of Himself; since outside of Him there is nothing that is not of Him, as dependent, so also to be changed with no difficulty, if He should will. 2. Neither would a rational Being freely and willingly transfer itself into a worse state: certainly not God, who loves Himself perfectly. But He will not be able to transfer Himself unto a better condition, because one that does not have will not give; but God, transferring Himself unto a better condition, would be obliged to confer upon Himself those perfections of which He would actually be destitute.
d. That which is added to God, or withdrawn from Him, will either pertain to His Infinite Perfection, or not: if not, neither will it pertain to God Himself. But if so, it is not liable to mutation. And indeed, no finite, created, dependent thing is able to be added to God; since He is infinite, uncreated, and independent. Now, what is infinite, uncreated, and independent is no more able to be added to God than God Himself, since besides God nothing infinite, uncreated, and independent exists.
ORIGEN, book I contra Celsum, page 17, Ὁ Ἰουδαίων καὶ Χριστιανῶν λόγος, ὁ τὸ ἄτρεπτον καὶ ἀναλλοίωτον τοῦ Θεοῦ τῆρῶν, —λέγων ἐν ταῖς πρὸς τὸ θεῖον εὐχαῖς· Σὺ δὲ ὁ αὐτὸς εἶ, The Doctrine of the Jews and the Christians, which preserves immutability and unchangeableness of God…says in supplications to Deity, Thou art the same. GREGORY NYSSEN, tractate II in Psalmos, chapter IV, opera, tome I, page 298, Μόνη κρείττων ἐστὶ τροπῆς τε καὶ ἀλλοιώσεως ἡ θεία φύσις. οὐ γὰρ ἔχει πρὸς ὅ, τι χρήσηται τῇ τροπῇ, τοῦ μὲν κακοῦ ἀνεπίδεκτος οὖσα διόλου· πρὸς δὲ τὸ κρείττον τραπῆναι μὴ δυναμένη. οὐκ ἔστι γὰρ πρὸς ὅ, τι δέξηται τὴν ἀλλοίωσιν. οὐ γὰρ ἔχει τὸ ἑαυτῆς κρείττον, πρὸς ὃ μεταβήσεται, The Divine Nature alone is beyond change and alteration: For it does not have anything that might require change, not admitting of any evil at all, and not being able to be changed into something stronger: For it is not that which might accept alteration: for it does not have anything stronger than itself toward which it might be turned.
 George Bull (1634-1710) was an Anglican theologian and Bishop of St. David’s. He was fully orthodox with respect to his Trinitarian theology, but heterodox with respect to his assertion of the necessity of good works for justification, and therefore sometimes accused of Socinianism.