We are talking about what is called in Christian theology “the incarnation” — that is, God becoming man, or taking on human nature, or as John put it, the “Word” becoming “flesh” (Jn. 1:14). The Latin word for flesh is caro, hence the doctrine of the in-car-nation of Christ—his taking on human flesh (nature).
The incarnation is one of the most perplexing mysteries of the Christian faith. There are a number of things in the faith that are very difficult for us to wrap our minds around, and many people stumble at this. They say they can’t believe what they can’t understand. But this has always seemed odd to me. It seems to me to be something we should expect – that the Almighty and Eternal God who made heaven and earth and everything in them, should be unable to be fully comprehended by his creatures.
Now with regard to Christ, we must carefully maintain two strands of Scriptural teaching. First, the Bible is very clear that Jesus is God. I’m not saying that he is the Father; but that with respect to his nature he is God. “In the beginning the Word was with God and the Word was God” (Jn. 1:1). “In him the whole fullness of deity dwells bodily” (Col. 2:9). And there are other passages teaching the same truth (e.g., Jn. 20:28; Rom. 9:5; Phil. 2:5-8; Tit. 2:13; Heb. 1:3, 8).
This is one strand of Scriptural teaching concerning Christ. The other is that he is human. John tells us that the Word became flesh and dwelt among us. Paul tells us that although Christ “was in the form of God, [he] did count equality with God a thing to be grasped, but made himself nothing, taking the form of a servant, being born in the likeness of men” (Phil. 2:5-6). In a very real sense, then, Jesus is Immanuel, “God with us.”
And the question is, “From whom did Jesus receive his human nature? Did he receive it from Mary, or did God create a human embryo to implant in Mary’s womb?”
Think about it like this: If God created a human embryo (or perhaps more exactly a human zygote), and implanted it in Mary’s womb so that re received nothing from Mary, then Jesus is not really a descendant of Adam. He is not really of Adam’s race, not to mention the fact that he is not really descended from David or Abraham.
But God had said way back in the garden, soon after the fall, that the seed of the woman would crush the serpent’s head. And he told Abraham that it was through his seed that all the families of the earth would be blessed. And he told David that he would raise up a descendant to sit on his throne. But if Jesus received nothing from Mary (with regard to his human nature), if God created a new human being from scratch as it were, then none of these promises would have been fulfilled.
The Council of Chalcedon in 451 is one of four ecumenical councils accepted by nearly all branches of Christendom. The council was convened specifically to consider the question of how the two natures (human and divine) of Christ relate to each other.
Following, then, the holy fathers, we unite in teaching all men to confess the one and same Son, our Lord Jesus Christ. This selfsame one is perfect both in deity and in humanity; truly God and truly man, with a rational soul and a body; consubstantial with the Father according to His deity, and consubstantial with us according to the humanity; like us in all respects, sin only excepted.Consubstantial means “of one and the same substance,” and the word is used to indicate the relationship Jesus has both to the Father and to the human race. He is of one and the same substance with the Father, and of one and the same substance with us.
The Council proceeded to say that Jesus is “to be acknowledged in two natures; without confusing them, without interchanging them, without dividing them, and without separating them.”
In the Westminster Confession of Faith, which is one of the clearest expressions of the Reformed faith, Jesus is described as “being conceived by the power of the Holy Ghost, in the womb of the virgin Mary, of her substance” (WCF 8.2)
This is the only way we can do justice to the teaching of Scripture. Jesus received his human nature from Mary, or at least a portion of it. If we want to get down to details, Mary must have contributed 23 chromosomes. But the other 23 chromosomes, those that would have come from a human father, were presumably created miraculously when the Holy Spirit came upon her, and the power of the Most High overshadowed her (Lk. 1:35)