How can the Incarnation be reconciled with Gods immutability? If God cannot change, then how can He become man?
The answer to this question rests on a distinction that runs through all the writers with remarkable consistency: the Incarnation involved no change in the Person of the Son — only a change in the form and condition He took. The eternal Son remained who He always was; what was new was that He took to Himself a true, full manhood, without ceasing to be God.
The Person unchanged, the form assumed
Hamilton Smith addresses this with particular precision in The Son of God:
Hamilton Smith"Scripture is careful to show that the Incarnation involves no change in the Person, and no addition to the Person, of the One who became incarnate. He was ever the Son and remains the Son. There was indeed a great change in the 'form' which He took, the 'likeness' in which He was found and the nature of which He partook, but there was no change as to His Person; Nothing that in grace He became, could add to, or take from, what He was."
Smith further clarifies what this means in practice — not two persons joined, but two natures in one Person:
"We do not see two persons united in Christ, as some have falsely taught, but two natures in One Person, which are surely distinct though nevermore to be viewed as separate."
"He, by birth, partook of human nature while ever remaining a Divine Person; we, by grace, partake of the divine nature while ever remaining human persons."
"Personality, whether human or divine, ever remains the same however much the conditions in which it may be found may vary."
Smith also quotes a fellow writer to drive the point home:
"There is no thought of a change in the Person, the real 'I'. He is always the same, though His 'form' is changed, and the condition in which He has life. When 'He' took part in flesh and blood who was 'He'? Personal identity does not change, though form and condition may."
And in his notes on Romans, Smith writes plainly:
"Christ is presented as the Son, speaking of His divine and eternal Personality, unchanged by anything He became."
The same Person from everlasting to everlasting
Smith presses the point further with this striking summary:
"'I AM' is the proper expression of His existence. While time rolls on 'I AM' remains unchanged, and when time has rolled away 'I AM' subsists the same." This is a true testimony in accord with the Scripture which declares "THOU REMAINEST" and "THOU ART THE SAME." The same glorious Person whether in the bosom of the Father, the womb of the virgin, or the arms of Simeon; whether in the manger of Bethlehem, the garden of Gethsemane, or on the Cross of Calvary; whether before the foundation of the world, through the ages of time, or when the world shall be no more. "FROM EVERLASTING TO EVERLASTING THOU ART GOD."
No change in the Godhead
J. McBroom, writing in Sonship by Incarnation or the Incarnation of the Son, approaches from the opposite direction — what would happen if the Incarnation did imply a change in God. His argument is devastating in its simplicity:
J. McBroom"Scripture shows that by Incarnation the Son became Man. This theory attempts to set it aside by asserting that by Incarnation a Divine Person became Son. This error involves something even worse, for if one Divine Person became Son by Incarnation then another became Father by the same act. Now, He who is Father ever remains in absolute Deity where there can be no change."
"This solemn negation would deny that we have a revelation of what God is, and supplant it by something which He became; some change in Godhead which is admitted to be impossible."
McBroom also quotes with approval the formulation:
"Scripture makes clear that His Person is eternal and changeless whether as in the form of God as in eternity, or as come in the flesh, or as glorified as Man at God's right hand, or as the subject Son in eternity to come. He is ever the same ... a divine title conveying the thought of eternal immutability."
How then could He be "under God"?
McBroom addresses the inevitable follow-up question — if the Son's Person was unchanged, how could He say both "I and my Father are one" and "My Father is greater than I"?
"It may be asked how a Divine Person could be in a position which is not one of absolute equality. The answer is, by His becoming a Man. The new position was the result of a new condition, that of Manhood. This condition and the position proper to it were perfect in their order, but taking these did not for a moment mean that the condition and position of Godhead were relinquished. When here in Manhood He was still unchanged in Person, co-equal and co-eternal in fulness of glory, majesty and splendour, GOD. But having become Man He was, in virtue of Manhood, under God."
The glory veiled, not diminished
J. G. Bellett, in The Son of God, traces how this truth plays out in the Gospel narratives. The divine glory was hidden under the form of a servant — not abandoned:
J. G. Bellett"And such was Jesus, 'God manifest in the flesh,' commonly veiled under 'the form of a servant,' always without robbery equal with God in the faith and worship of His saints, and at times shining forth in divine grace and authority."
"The Person in the manger was the same as on the cross. It was 'God manifest in the flesh.' And in the full sense of that glory we can but speak of His humbling of Himself from the earliest to the latest moment of that wondrous journey."
Bellett notes that Christ's self-emptying was not a surrender of deity, but an act worthy of deity:
"He emptied Himself for all this, but all that He did was infinitely worthy of His person."
And in his shorter piece, Jesus Christ come in flesh, Bellett makes an observation that cuts to the heart of the question:
"The very adjunct, 'come in the flesh,' throws strongly forward the deity of Christ; because if He were a man, or anything short of what He is, it would be no such wonder that He should come in the flesh."
The phrase "come in flesh" would be meaningless unless the One who came already existed in another mode of being — a mode so far above flesh that the coming was itself the marvel.
"Thou remainest... Thou art the same"
Writing in the Bible Treasury on Hebrews 13:8, a contributor traces this immutability through the entire epistle:
Bible Treasury"His person as God is the foundation of all His offices and works. In this way the Epistle opens with the most glorious proclamation of this truth. Heaven and earth pass away, but Christ does not."
"Thou, LORD, in the beginning hast laid the foundations of the earth; and the heavens are the work of thine hands; they shall perish, but thou remainest; and they all shall wax old as doth a garment, and as a vesture shalt thou fold them up, and they shall be changed; but thou art the same, and thy years shall not fail."
And another Bible Treasury writer, commenting on Hebrews 1-2, observes:
"In Hebrews 1-2, THE SON is remarkably brought before us; in chapter 1 as to His eternal Godhead, and in chapter 2 as to His manhood. Yet not exclusively so in either chapter, for how could this blessed One, who is both God and man in one person, be divided? Perhaps there has not been a more fruitful source of error than the attempt to do this."
A mystery beyond us — received, not explained
Hamilton Smith concludes with a word of solemn caution that all the writers share:
Hamilton Smith"How a divine Person can come in flesh we do not know. We have to beware of any statement which seeks to make clear to the human mind the inscrutable mystery of the incarnation. Any statement with this avowed end should at once arouse our suspicion. We may be sure that any such attempt will not only fail of its purpose but will end in propounding theories that corrupt the truth and dishonour the Son."
The answer, then, is not that the difficulty is dissolved, but that it is rightly located. God did not change. The eternal Son — the "I AM" — took to Himself something new: a real, full humanity of spirit, soul, and body. What He was, He remained. What He became, He added. The divine Person was not altered; He entered a new condition. The "form of God" was hidden under "the form of a servant," but it was hidden, not surrendered. The glory was veiled in flesh, not exchanged for it. And precisely because the Person who came in flesh was God, the coming was the supreme wonder — for had He been anything less, it would have been no wonder at all.