The Incarnation cannot be undone. If it could, it would be the undoing of our salvation, for the Cross and Resurrection would be of no benefit to anyone. Nor could it be undone for some without undoing it for all. It is all of one piece, just as humankind is, for we all partake of human being, the one and only way of being human.
When Christ the Word became “flesh” and dwelt among us (John 1:14), he did not merely put on human being as a suit, which could later be discarded when it served its purpose. No, he became human being, and is so eternally. He defines what it means to be fully human — yet he did not cease to be fully divine.
Nor did Christ become merely a singular instance of human being. That, too, would have done us no good, for his actions would have been of benefit only to himself. But he became human in such a way that in his death all died, so that in his resurrection all might be raised.
In Romans 5:18, St. Paul compares/contrasts Adam and Christ. “Consequently, just as one trespass [Adam’s] resulted in condemnation for all people, so also one righteous act [Christ’s] resulted in justification and life for all people.” Just as the connection between Adam and humankind was universal, such that Adam’s disobedience resulted in condemnation for all, so also the connection between Jesus Christ and humankind is universal, such that Christ’s obedience has resulted in justification and life for all.
Likewise, in 1 Corinthians 15:22, “For just as in Adam all die, so also in Christ all will be made alive.” Just as the connection between Adam and humankind was universal, such that in Adam all die, so also the connection between Jesus Christ and humankind is such that in him all will be made alive.
By the Incarnation, Christ is united, eternally and inextricably, with us all. For humankind, which was once headed up in Adam, is now headed up in Christ.