The relationship of the two natures of our one Mediator is called the Hypostatic Union. These words simply mean “a union of two substances” or “a personal union.”

While we ought not to get bogged down with all kinds of strange terms there are some which we must know if this truth is to make any sense at all to us.

One term is nature. By nature we mean the sum-total of all the essential qualities of a being. Other words which are used in place of nature in discussions of the Mediator are “essence,” “being” and “substance.” To put it in other words, nature is what makes a being what it is. Thus, our Mediator has a human nature and a divine nature because He is both God and Man.

The other term we must understand is person. By person we mean an independent, individual subsistence (a living being) who has the ability to reason and who is responsible for his own actions. The person is that which says “I.” In other words, a person is a rational, moral being.

We do not confess that Christ is two persons, but that He is two substances or natures in one person. The relationship of these two substances or natures is called the Hypostatic Union. This union is personal because through the Incarnation the Second Person of the Trinity established a personal union between Himself and a human soul and body. John Murray wrote: “The incarnation means that he who never began to be in his specific identity as Son of God, began to be what he eternally was not” (Collected Writings, II, 132).

Of this we read in John 1:14, “And the Word became flesh, and dwelt among us . . . .” When we say that the Word became flesh we do not mean that the Son of God ceased to be God and was converted into a human being alone. God. did not change Himself into man. Instead, it means that the Word came to possess a new nature without abandoning the first. Only then could it be said. that “we beheld his glory, glory as of the only begotten from the Father” (v. 14).

As hard as this is to understand, we must carefully state what the Church has always believed on the basis of God’s revelation in Scripture—and it must be done with care or we risk opening the door to heresy. The Westminster Confession put it this way: “Two whole perfect, and distinct natures, the Godhead and the manhood, were inseparably joined together in one person, without conversion, composition, or confusion” (VIII, ii).

1. The person of the Son of God. is inseparably united with the human nature. This union is without mixture or fusion.

The fathers at Chalcedon tried to illustrate what they meant by this by pointing to iron made hot by fire. The fire and iron seemed to become one. You cannot distinguish the fire from the iron or the iron from the fire. Yet, neither loses its own properties. Also, they pointed to the union of the human soul and body. Both of these illustrations begin to show something of the relationship of the two natures of Christ, but they can go no further. Ultimately they will fail, as all illustrations do, to thoroughly clarify this truth.

Once these two natures are united they can never be separated—except in our thought.

William G. T. Shedd wrote: When the infant Jesus lay in the manger, the Logos was present and united with the human nature as really and completely as he is this instant, but he made no exhibition of himself. There was no more thinking going on in the infant human mind. of Jesus, than in the case of any other infant. The babe lay in the manger unconscious and.inactive. Yet the eternal Logos was personally united with this infant. There was a God-man in the manger as truly as there was upon the cross (Dogmatics, II, 275).

Even in d.eath this union was not destroyed. True, the union of the human soul and. human body was dissolved temporarily through the death on Calvary, but the union of the Divine and human natures was not.

Scripture never spells out this relationship, it is assumed. just as is the relationship of the three persons of the Trinity. However, there are many telling footprints of this relationship.

There is no distinction mad.e between the two natures by our Lord. He never says, “I speak as God,” or “I speak as man.” What is said.as true of the Divine nature, is true of the Person of Christ (John 8:58, 17:5). What is said as true of the human nature, is true of the Person, also (John 19:28, 11:35; I Corinthians 2:8).

Divine qualities and actions are ascribed to Christ in connection with human titles given to Him (John 3:13, 6:62; Romans 9:5; Ephesians 1:23; Acts 17:31).

Human qualities and actions are also ascribed.to Christ in connection with Divine titles given to Him (Luke 1:31, 32, 35; Acts 20:28; I Corinthians 2:8; Colossians 1:13–29; Hebrews 1:3).

Of this union, Thomas Watson (cf. c1690), known for his rectorship at St. Stephen’s Wallbrook, London and later for leaving the Establishment because I of the Act of Uniformity, wrote:

This union of the two natures in Christ was not by transmutation, the divine nature changed into the human, or the human into the divine; nor by mixture, the two natures mingled together, as wine and water are mixed; but both the natures of Christ remain distinct, and yet make not two distinct persons, but one person; the human nature not God, yet one with God.(Body of Divinity, p. 114).

2. These two natures—human and.divine—are united in one single person.

There are not two Sons of God. Nor is the human nature incomplete or imperfect. Further, they are united inseparably. However, the divine nature is still divine and the human nature is still human.

3. Both natures retain their own distinct properties. Commenting on this, John Murray wrote:

If there had been some kind.of transfer of human properties to the divine nature, then the Lord Jesus Christ would have ceased to be truly God. If there had been some kind of transfer of divine properties to the human nature he would not have been truly man. In the one case he would no longer be the eternal Son of God and equal with God. In the other case he would not be of one flesh with us, made in the likeness of sinful flesh, clothed with our nature and the High Priest endued with a feeling of our infirmities, tempted in all points like as we are, yet without sin. Hence the preciousness of the statement, “two distinct natures, and one person, for ever” (Collected Writings, I, 34).

Now admittedly, this is all very difficult for our minds. And while this truth is taught in Scripture it seems somewhat impractical as we think about it. But is it really so impractical?

First, unless our Mediator is this kind of person He could not have made the one and perfect offering for sin. In order for Him to save us the atonement has to be the act of His whole person. To be my Substitute He must be true man and at the very same time He must be God. All of His acts are the acts of His whole person: eating, raising the dead., forgiving . . . and atoning. In His atoning death He could experience God.‘s wrath on sin only because He is God and man. And then, being God.and man, death would.not destroy Him. Rather, He would.conquer death for us. Therefore, we testify, “Jesus, my God, Thy blood alone has power sufficient to atone.”

Second. because the Son of God is this kind of person He can sympathize with His people (Hebrews 4:15). He was tempted, touched by our infirmities and subject to the Law, as we are. He “knows our every weakness.” Because He is both man and the God of Grace we can “draw near with boldness unto the throne of grace, that we may receive mercy, and find grace to help us in the time of need” (Hebrews 4:16). If He were not this kind of person we would not have this comfort.

Besides, because He is the God-Man, He is our source of life. We, therefore, can testify with Paul, “I have been crucified with Christ; and it is no longer I that live, but Christ liveth in me: and that life which I now live in the flesh I live in faith, the faith which.is in the Son of God, who loved me, and gave himself up for me” (Galatians 2:20).

Indeed, if our Mediator is not God and man in one person we would. not know salvation nor any of its blessings. Since He is, we can say:

Jesus, my God, I know his name, His name is all my trust; Nor will He put my soul to shame, Nor let my hope be lost.