of [Israel] are the fathers and from [Israel], according to the flesh, Christ came, who is over all, the eternally blessed God. Amen. Romans 9:5NKJV
Question 37 of the Larger Catechism asks, “How did Christ, being the Son of God, become man?” It gives the answer, “Christ the Son of God became man, by taking to himself a true body, and a reasonable soul, being conceived by the power of the Holy Ghost in the womb of the Virgin Mary, of her substance, and born of her, yet without sin.” Last time we examined the Biblical teaching that the God-man Jesus is the one and only Mediator of the Covenant of Grace, from the Fall in the Garden of Eden unto forevermore. This week we consider how it was that Jesus, the infinite and eternal second person of the Holy Trinity, became a finite and temporal human being.
First, when the Catechism says that Christ became a man, it is not denying that He continues to be God. As we saw last week, the answer to question 36 declared that Jesus Christ “in the fullness of time became man, and so was and continues to be God and man, in two entire distinct natures, and one person, forever.” Thus, the Catechism rightly teaches that Jesus did not change His nature from divine to human. He, who was God by nature, when the fullness of time came, took upon Himself the additional nature of a man. The phrase “in the fullness of time” is a direct reference to Gal. 4:4: “But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law.” At a certain point in time, Jesus, the eternal son of God, was sent by the Father to be born as an ordinary human being. As the Scripture at the head of this article declares: Christ, who is the eternally blessed God (His divine nature), came from Israel, according to the flesh (His human nature).
In other words, He who was always fully God is now also fully man. Therefore, since He was fully man, Jesus took upon Himself not only a human body but a human soul. The Catechism calls it a “reasonable soul,” since theologians have traditionally appealed to reason as the chief faculty that distinguishes man from the animals. As Augustine declared in The Soul and Its Origin, “man is endowed with reason and capable of intelligence, which, of course, animals void of reason are not.” Thus, also the great Creed of Chalcedon (451), “We … confess one and the same Son, our Lord Jesus Christ … truly God and truly man, of a reasonable soul and body.”
The Creed was in part addressing the 4th century heretic, Apollinaris, who taught that while Jesus took on a human body and a human soul, the mind or reason of His humanity was replaced by the divine logos. Although Apollinaris was mistaken in his tri-partite (3 part) view of man, his real heresy was in denying the full humanity of Jesus Christ. For, if there was any part of man that Jesus did not take upon Himself in His incarnation, then He was not fully human. If He was not fully human, then He could not have vicariously taken upon Himself the wrath of God, due to sinful humans, and He could not have vicariously performed the moral righteousness, owed to God by humans. Simply put, only a savior who is fully man can satisfy God for man’s sake. Jesus was man in every way, just as we are, except He alone was without sin (Heb. 4:15).
The final part of today’s question declares how the eternal Son of God became a man. How did the divine nature of Jesus Christ become joined to a human nature in one person? By an immediate work of God. The Holy Spirit conceived the human nature of Jesus in Mary’s womb, while she was still a virgin. Jesus’ conception was supernatural. There was no naturally generated human sperm that united with Mary’s naturally generated human egg. It is very important that we affirm that Jesus was “of the substance of Mary,” for he was truly human, and therefore, His human nature must come entirely from Adam, as every other person does. And therefore, He had to develop in the womb, from conception on, and be born and grow in body and mind, just as every other person does. But the Father of Jesus’ human nature was not a man, it was God. As the angel said to Mary, “The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God,” (Luke 1:35).