Modalism and all its variations face a significant problem in the incarnation of the Lord Jesus Christ. These theologies teach that the Son of God is the same individual being as the Father; they are together the one God, the same sole Supreme Being. The Son, in these views, is just as much the one God as the Father is. But if that is so- if the Lord Jesus Christ is Himself a person, mode, subsistence, or part of the Supreme Being in some way, can He also be a man?
The answer we are forced to by scripture is a resounding ‘no’. Consider the following:
1) The one God declares that He is not a man: “God is not a man, that He should lie, Nor a son of man, that He should repent;” (Numbers 23:19 NASB); He also declares that He never changes: “For I, the Lord, do not change” (Malachi 3:6 NASB); thus is follows, that if it was once true of Him that He was not a man, then it is true of Him always, eternally and unchangingly, that He is never a man. For if He went from not being a man to being a man, this would, undeniably, be a change; and so it follows that in order for Him to have become man, He will either need to be mutable, or else, if God is immutable, He will either need to have always been a man. And if He is immutable, and has not always been man, then if follows necessarily that He is never a man. We know that He is immutable; and we know there was a time when He was not a man; and so, He cannot have always been a man. And so the remaining option must be true, that the one God never is and never will be a man. And so, the one Who became incarnate in Jesus of Nazareth, cannot possibly have been the one God.
2) The one God is invisible; no one has ever seen Him, and no one can see Him: “No one has seen God at any time” (1 John 4:12 NASB), “who alone possesses immortality and dwells in unapproachable light, whom no man has seen or can see.” (1 Timothy 6:16 NASB); yet, the Lord Jesus Christ, as a man, was undoubtedly seen: “What was from the beginning, what we have heard, what we have seen with our eyes” (1 John 1:1 NASB). And so, were the Supreme Being incarnate, the Supreme Being would very much have been seen, a thing which scripture repeatedly declares has never, and indeed, cannot, occur. And if it is objected to that only a human part of the Lord Jesus was seen, this will not help; for we will ask, was this human part united to the one incarnated so as to be part of His own person, or not? If not, then the being in question was never incarnated at all; if yes, then it follows that the one incarnated was seen in His own person, since the humanity was part of His own person. And so, if the one incarnated was the Supreme Being, then the Supreme Being was, in His own person, seen by men; a thing which scripture repeatedly denies has ever occurred.
3) The one God is immortal: “who alone possesses immortality and dwells in unapproachable light” (1 Timothy 6:16 NASB); to be man involves being mortal, and certainly, as the Lord Jesus Christ died for our sins, His mortality was proved beyond doubt. He cannot then be the Supreme Being, for this would be to assert that He that is incapable of ever dying, died. And while some modalists rejoice in such contradictions, and declare them heavenly mysteries, they ought not; for a contradiction which arises from incoherent interpretations, theories, and inferences, is not so much a mystery as a plain contradiction, and, as it stems not from divine revelation but human reasoning, it cannot be called heavenly, but is earthly and human. For the scriptures never once assert that the immortal Supreme Being, the only true God, was incarnate in the Lord Jesus, or that the one God died. Rather they declare that the one God is another besides the Lord Jesus, the Father of the Lord, and that He is wholly incapable of dying. And so it was not the one God, the Supreme Being, Who died on the cross as a man, but another, namely, His Son.
It follows clearly from these considerations that the one God is not, and never has been, in part or whole, a man; and therefore, that the one incarnated in Jesus of Nazareth is not the one God, the Supreme Being, but another, the Son of that one God.