This question is part of a bigger one: How do we understand the mystery of the Incarnation itself? When I say mystery, I'm using theology's label for any divine reality that we know is actual (because the Bible tells us so) while not knowing how it is possible (since it outstrips our minds). We know it by faith, taking God's Word for it, and see it as above (but not against) reason. The Trinity, God's sovereignty over human freedom, and our union with the risen Christ in new birth are examples. So is the incarnation of the Son of God.
The Incarnation, meaning "enfleshing," is the event that the Apostle John announced by saying "the Word became flesh" (Jn. 1:14). The concept is not that the Son put on a human body as one puts on an overcoat, nor that a human being and a divine person lived together under one skin, nor that a divine person came to possess two sets of powers (natures), each of which he could switch on or off as he chose.
It is, rather, that first in Mary's womb, and then in this world, and now forever in heaven, the Son lives life through the mind-body complex that constitutes humanity—bypassing none of it, even when drawing directly on divine power or intuiting directly the Father's mind and will. Without diminishing his divinity, he added to it all that is involved in being human.
When Jesus is hailed as one person in two natures, according to the Council of Chalcedon in 451, this is what is meant. So by incarnation the Son became more than he was before, and a human element became integral to the ongoing life of the Triune God. Being as fully human as divine became one strand of the Son's identity, destiny, and glory. Evangelicals, Orthodox, and Catholics unite in believing this.
The biblical and theological ...