There have been many broken and flawed Christologies over the years, and in truth many of them continue to crop up in mainstream evangelicalism. Nearly every major heresy the church confronts (and no few of its littler skirmishes) revolve around issues of the nature of the Incarnate Son of God. From the earliest days of the church, there has been a tension between those emphasizing Jesus’ humanity at the cost of his deity and those emphasizing his deity at the cost of his humanity. The clear testimony of Scripture, however, is that Jesus was everything that it is to be God and also everything that it is to be human.
When we say, then, that in the Incarnation the Son of God ‘took his flesh from Mary’, we are emphasizing that he inherited from her all that it means to be a human being. Nothing was missing or absent. The Word who was from the beginning, and through whom the Father created the world, and indeed for whom the world exists, took upon himself human body and soul/mind/spirit.
He participated fully in all the weaknesses of human existence. He became subject to common colds and the need to expel waste from his body. He experienced teething pains, and he needed to eat and sleep. He experienced real temptation to sin, more fully than has any other human because he resisted it to the last. He bore the sorrows of life in a world filled with suffering and war and death. He was in everything the word means human. As the author of Hebrews puts it:
Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery. For surely it is not angels that he helps, but he helps the offspring of Abraham. Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people. For because he himself has suffered when tempted, he is able to help those who are being tempted. (Hebrews 2:14–18)
We share in flesh and blood; he shared in flesh and blood. He became like us in every respect—not partially, not in some respects, but in every respect. He suffered when he was tempted; the lures and draws of the world did not simply pass by him without any challenge whatsoever. He took from Mary everything about humanity.
This matters because, as the Fathers pointed out, what he has not assumed has not been redeemed. Redemption is more than (though of course not less than) propitiation for sins. It is the re-uniting of humanity with God, so that all the myriad ways in which human nature has been broken may be set once again how it ought to be. It is the restoration of all the things that were broken in humanity by the Fall. There is no part of humanity that was not broken by the Fall, no part that does not need restoration, no part that was not cut off from fellowship with God. Thus, there is no part of humanity that is not in need of redemption, and so anything the Son did not take up of our humanity when he became Jesus the Christ is still broken.
If Jesus had only the mind of God and not a human mind, then our minds are still unredeemed. If Jesus’ body was not the Son’s body but a drone-like extension of his will, then our minds remain unredeemed. If Jesus’ will was not a human will but purely and only a divine will, then our wills remain unredeemed. In each case, if Jesus was not both God and man in his nature, we are lost. In this sense, then, few things are of more theological import than the nature of the incarnation. The cross and resurrection, powerful though they are, do not have their intended effect of redeeming lost women and men unless the Incarnation was the complete joining of God and man in Jesus. And so: praise be to God! For when Jesus took his flesh from Mary, he took up humanity whole and entire, leaving nothing out, and joined it with his deity whole and entire, leaving nothing out. So now we through him participated in the divine nature (2 Peter 1:4), just as he participated in human nature.