What does it mean to say, “Christ assumed human nature?” Sure, assumption comes into view, but what did Christ assume? The question of nature is an important one, for two major reasons. First, we’re a generally metaphysically illiterate generation. Substance, essence, and nature are all words we’ve heard and used, but are typically ignorant as to their significance. Second, “nature” is a central concept in at least three foundational Christian doctrines: the doctrine of God, the doctrine of creation, and the doctrine of Christ. To misunderstand and misappropriate the concept of nature is to risk serious errors (if not heresies) regarding each of these doctrines.
To get started, we might define nature as the “what” of a thing. When we ask, “What is an automobile?” we inquire into the nature of automobiles. When we ask, “What is man?” we ask the question of humanity or human nature. Bernard Wuellner offers the following definition relevant to our purposes here, that nature is “the essence or substance considered as the intrinsic principle of activity and passion or of motion and rest.” Nature, in this case, explains why this thing is the way that it is and why it does what it does. The nature of an elephant distinguishes it from a giraffe, an alligator, and so on. Things differ in their natures. Things differ because of their natures.
When we speak of an elephantine nature, we speak of something different than a birdly nature. Why? Because the essential properties of an elephant distinguish it from birds. Elephants and birds have different properties that distinguish their species. When we speak of human nature, we speak of that which distinguishes man from beast. What is human nature as distinct from an elephantine nature? The essential properties differ. The essential property of man distinguishing him from all lower life forms is his intellectual soul. The intellectual soul, or the intellect and will of man, is what sets man apart as the highest of God’s creatures, second only to angels.
Concerning this intellectual or rational soul, Peter Van Mastricht lists three things it entails, “In the rational soul is intellect, will, and free choice.” The intellect is the reason, in which we find self-awareness and the power of discursive reasoning, i.e. the ability to reason from one fact to another and to see things in relation to the whole. Van Mastricht refers to it as the power of “apprehending the true.” Judgment pertains to the intellect, affirming and denying propositions, suggestions, or actions as either true or false, either just or unjust.
The second faculty is the will. Animals also possess wills, but their wills are led along by what is called a sensitive appetite. They only will what is required to satisfy their sensitive appetite, and this results in survival. Man, on the other hand, has not only a sensitive appetite, but also a rational appetite, or the intellect, which the will should follow.
The will of man is to chiefly follow the intellect, according to knowledge. And this ought to result in holiness and righteousness. Hence, knowledge, holiness, and righteousness are the three virtues according to which man images God, “After God had made all other creatures, he created man, male and female, with reasonable and immortal souls, rendering them fit unto that life to God for which they were created; being made after the image of God, in knowledge, righteousness, and true holiness…” (2LBCF, 4.2)
Fallen Human Nature
Human nature, considered by itself, is good—having been created by God who is goodness. Upon the entrance of sin, however, that nature is said to be depraved, that is, the good of human nature has been corrupted, perverted, or twisted from its original constitution. In this corruption, both the intellect and will are darkened, or lack the light with which they were originally created. But this fallenness is by no means essential to man. In other words, this fallenness is not an essential property of humanity. It’s not part of the original human nature. Man can be conceived of without a sinful nature. Indeed, man’s first state did not include the fallen nature. And his final state will not include the fallen nature. Yet, he will nevertheless remain human.
When we say, then, that our Lord “assumed a human nature,” we mean to say that He assumed all that pertains essentially to humanity, with the obvious exception of sin. (Heb. 4:15) And this brings us to our final and central consideration—
The Human Nature of Christ
I quote the whole of 2LBCF 8.2—
The Son of God, the second person in the Holy Trinity, being very and eternal God, the brightness of the Father’s glory, of one substance and equal with him who made the world, who upholdeth and governeth all things he hath made, did, when the fullness of time was come, take upon him man’s nature, with all the essential properties and common infirmities thereof, yet without sin; being conceived by the Holy Spirit in the womb of the Virgin Mary, the Holy Spirit coming down upon her: and the power of the Most High overshadowing her; and so was made of a woman of the tribe of Judah, of the seed of Abraham and David according to the Scriptures; so that two whole, perfect, and distinct natures were inseparably joined together in one person, without conversion, composition, or confusion; which person is very God and very man, yet one Christ, the only mediator between God and man.
There are several observations we should make. First, the Son is a divine Person. He is essentially God. There is no real distinction between the Person of the Son and the divine essence. The Son is “very and eternal God…” This means the Son is “of one substance and equal with him who made the world…” Though the Son is distinct from the Father in His manner of subsistence, i.e. begottenness rather than unbegottenness. Yet, neither are distinct from the essence. For this reason Father, Son, and Holy Spirit are said to be consubstantial, that is, of a numerically single substance, one essence, or of the same nature.
All that may be said of God must be said of the Son. In fact, excepting only the peculiar properties which distinguish their manner of subsistence, all that may be said of the Father may be said of the Son and Spirit. Why? Because they are a single divine essence. Their what (nature or essence) is the same, though they are distinguished in view of the threefold way in which that one essence eternally subsists.
Second, the Son “when the fullness of time was come, [did] take upon him man’s nature…” This clause describes the notion of assumption. Dr. James Dolezal, in his paper ‘Neither Subtraction, Nor Addition: The Word’s Terminative Assumption of a Human Nature’, delineates three distinct types of assumption: divestive assumption, augmentative assumption, and terminative assumption. Divestive assumption entails kenotic theory, where it is said the Son divested Himself of His deity in the assumption of human nature. In other words, the Son loses something proper to His deity. Augmentative assumption would entail the addition of humanity to His deity. He added something He did not have before.
Regarding terminative assumption as the more adequate doctrine, Dolezal writes, “The principal claim is that the person of the Word terminates—in the sense of completing or perfecting—the assumed human nature by bringing it to his own subsistence and thereby supplying to it the personhood it requires for its existence.”
This is not an essay on terminative assumption. However, I survey the concept only to say: The Son assumed the fullness of human nature, and He did so terminatively. He did not lose, suspend, or lay aside anything proper to His divine nature. Neither did He augment His deity by adding something to it. As technical as the above sounds, it is but the doctrine of immutability consistently applied in Christology.
Third, because our Lord did truly assume a human nature, He assumes with it all the essential properties of human nature. As the Confession states, “…with all the essential properties and common infirmities thereof, yet without sin…” This entails a human body, but it also entails a rational soul, with its intellect and will. In answer to Q. 25 of the Baptist Catechism, we read, “Christ the Son of God became man by taking to himself a true body (Heb. 2:14, 17; 10:5), and a reasonable soul (Mt. 26:38); being conceived by the power of the Holy Spirit in the womb of the Virgin Mary, and born of her (Luke 1:27, 31, 34, 35, 42; Gal. 4:4), yet without sin (Heb. 4:15; 7:26).”
The very God-ness and very man-ness of Christ is confused in many modern conceptions of Christology. Many Christians do not know how to speak of the hypostatic union in such a way that they preserve both natures—divine and human. The hypostatic union entails the following: All that may be said of God must be said of Christ, and all that may be said of man (except for sin) must also be said of Christ. If Christ is truly human, then He truly possesses a human body, a human soul with a human intellect and will. All of this He has in union with His undivested and unmanipulated deity. His deity remains the same, “without conversion, composition, or confusion…” to or with His humanity. So, the Person of Christ is both very God and very man—two perfect and complete natures united in the second Person of the Holy Trinity.
The doctrine of the hypostatic union prevents us from confusing the deity and humanity of Christ. We must remember that deity does not pray, eat, or suffer. Thus, the Person of the Son assumed a nature capable of these kinds of actions, i.e. a human nature. That which is proper to deity belongs to His divine nature while that which is proper to humanity belongs to His human nature. When our Lord tells us that He is “I AM,” He is using language proper only to His divine nature, that is, as Yahweh—though He speaks as a man. Conversely, when our Lord prays, eats, or suffers He does these things according to the nature capable of suffering—His humanity. When we fail to properly parse the two natures of Christ, we blur the Creator/creature distinction—assigning creaturely traits to deity, and divine traits to humanity. But we must confess that pantheism remains untrue, even in the Person of Christ.
Nature refers to the what-ness of a thing. We might say that the one Person of Christ has two “whats,” or two natures—divine and human. These natures remain distinct, yet united. When we speak of Christ, we predicate things concerning His Person that are proper to one or the other nature. That Christ is omniscient is not proper to His humanity, but only to His deity. That Christ mourned and prayed is not proper to His deity, but only to His humanity. Ignoring this distinction leads to a confusion of the two natures, God with man, which is nothing less nor more than pantheism. Christ, therefore, was truly man. All that which is proper to a human nature may be predicated of the Person of the Son—a human body, a human soul, a human intellect and will. All of this is true while He is yet very God.
 Bernard Wuellner, Dictionary of Scholastic Philosophy, (MIlwaukee, WI: The Bruce Publishing Co., 2012), 79.
 Peter Van Mastricht, Theoretical-Practical Theology, vol. III, (Grand Rapids, MI: Reformation Heritage Bookks, 2021), 257.
 James Dolezal, ‘Neither Subtraction, Nor Addition: The Word’s Terminative Assumption of a Human Nature’, https://www.academia.edu/63681891/Neither_Subtraction_Nor_Addition_The_Words_Terminative_Assumption_of_a_Human_Nature