The following is taken from an article by James Anderson which was entitled 3 Christmas mysteries. In the article this was the first of them with the heading -The Incarnation of the Son of God. If you want to read of the other 2 mysteries you can access the whole article here: https://www.thegospelcoalition.org/article/3-christmas-mysteries

James Anderson is associate professor of theology and philosophy at Reformed Theological Seminary in Charlotte.

The Word became flesh and dwelt among us. (John 1:14)

“The Word became flesh.” Those four words can sound so familiar to us that we fail to appreciate the magnitude of John’s statement (echoed by the other New Testament writers). The divine (v. 1) became human (v. 14). The infinite, omnipotent, omniscient, omnipresent Son of God took on a human nature: finite, limited in power, limited in knowledge, limited in space and time. It’s one thing to claim God would ever do such a thing. It’s yet another to suppose God could ever do such a thing—that he could clothe himself with frail humanity, veiling his divine glory without relinquishing for one moment any aspect of his divine nature. The Danish Lutheran philosopher Søren Kierkegaard referred to the incarnation as the “absolute paradox” of the Christian faith. How could the eternal inhabit the temporal? How could the finite accommodate the infinite?

We may not know how this mystery could be reality, but by the testimony of inspired Scripture we know with certainty (Luke 1:4) it was and is reality. This is a mystery of the first order.