The Incarnation is a mystery because we do not have the depth of rational thinking necessary to comprehend it. Your question is a good one. Let’s review some of the biblical evidence indicating that the incarnation of the Son of God will be preserved throughout eternity. Then I will list a few theological reasons for addressing your concern.
1. The Perpetuity of the Incarnation
The biblical evidence is clear: the union of the human and divine natures of Christ is unbreakable. “The Word became flesh” (John 1:14) and was “born of a woman” (Gal. 4:4). He grew up as a human being (Luke 2:40) and remained so throughout His ministry (Heb. 5:7). During His crucifixion human blood came out of Jesus’ hands and forehead; He was thirsty (John 19:28) and felt abandoned by God (Matt. 27:46). Like all human beings, He finally died (John 19:30). He came from the tomb as a human being in a glorified body (John 20:27) and was seen by Mary (verse 18) and the disciples (John 21:1). Christ ascended to heaven with His human, physical body, taking human nature to the throne of God (Acts 1:11). He now intercedes for us before the Father: “For there is one God and one Mediator between God and men [anthrōpōn, “human beings”], the Man [anthrōpos, “human being”] Christ Jesus” (1 Tim. 2:5).
John affirms what false prophets deny, namely that “Jesus Christ [is] coming in the flesh” (2 John 7). Paul adds that once the cosmic conflict is over, all things will again be subject to the Father, and “the Son Himself also will be subjected to the One who subjected all things to Him, so that God be all in all” (1 Cor. 15:28, NASB).* The Incarnation will never be suspended. Christ became human forever. His sacrifice is an eternal one.
2. One Incarnated SavioUr
The perpetuity of the Incarnation reflects the very nature of the Incarnation. If it were not eternal, we would not have an Incarnation but only a temporary indwelling of God in a human being. The Incarnation is in fact two natures in one person, not two persons dwelling together who could easily separate from each other whenever they wished. Jesus does not exist independent of the Incarnation. In Him the human and the divine coexist in an unbreakable union, making it possible for us to be united with God once again.
This divine saving act will always be a reality in the universe. The end of the Incarnation would be the end of our divine-human Saviour. It is simply impossible for this to happen. He is, and will remain forever, our Saviour. What happened in the Incarnation was not something that could be undone once it accomplished its purpose.
3. End of Sin and Perpetuity of the Incarnation
In exploring the permanent nature of the Incarnation, we should also consider the fact that sin is both a cosmic and temporal phenomenon, and that its resolution is also cosmic and temporal. Through the work of Christ sin will be eliminated from the universe (cosmos) forever (the time element) and will never rise again. The solution to the sin problem is cosmic and permanent. It is not only a historical event that happened at a particular time in the past—God’s saving act is an ever-present and eternally effective event.
The humiliation of God in becoming human in order to die for a sinful race is eternally preserved to ensure that sin will not rise again. The Incarnation is part of Christ’s sacrifice for us.
*Scripture quotations marked NASB are from the New American Standard Bible, copyright © 1960, 1962, 1963, 1968, 1971, 1972, 1973, 1975, 1977, 1995 by The Lockman Foundation. Used by permission.