Building on this, we notice a further integration that Vos develops with Christology and Covenant: he grounds the stability and certainty of the covenant of grace in the hypostatic union. By this union we affirm that the divine person (the Logos) assumed a human nature. It was not the union of a divine person and a human person, but the union of the divine nature and a human nature in the divine person of the Logos. In possession of both a true humanity and true divinity, he was fully God and fully man, the God-man. This person, and no other, is the Mediator and Surety of the covenant of grace.

The question, then, is what impact does Christ being a divine person, the God-man, have on the covenant of grace? Or, how does the covenant of grace differ from the covenant of works by having Christ as its Mediator? While the church has always affirmed and defended the necessity of Christ being both truly God and truly man (see e.g., Heidelberg Catechism Lord’s Day 6), the implications are sometimes left unturned.

Vos will argue that the covenant of grace derives its certainty not in the abstract, but from the person of its Mediator.

Only because the divine person is the subject in Christ does His mediatorial work obtain the stability required by an eternal, immutable covenant of grace. We now know, however, that this human nature in itself is an abstraction that did not exist for a moment without personal subsistence in the Logos (48).

Note, first, the careful distinction Vos makes between person and nature. He is not saying that the attribute of immutability that belonged to the divine nature was communicated to the human nature.[1] The divine nature remains divine and the human nature remains human. The unity of the two natures lies solely in the divine person of the Logos (see p. 42).[2] Again, the Logos did not assume a human person but a human nature. On this basis, Vos can write, “[I]n Christ’s human nature there was not a mutable human person but the person of the Son of God. Will or intellect or emotion in the human nature could not have sinned unless the underlying person had fallen from a state of moral rectitude. There can naturally be no thought of the latter for the Mediator, considering the deity of His person” (58).

Second, note how Vos understands the covenant of grace as eternal and immutable to require a certain kind of mediatorial work, namely one that is stable. Where does this stability come from? Vos says it comes from the Mediator being a divine person; particularly, from the human nature subsisting in the Logos, the second person of the Trinity. “The human nature of the Mediator did not exist for an instant apart from the person of the Son” (62). In short, the immutable nature of the covenant of grace required the assumption of a human nature by none other than an immutable divine person.

So Vos goes on to say,

Thus the person of the Logos with its personality provides His human nature with the steadfastness and immutability by which the covenant of grace is distinguished from the first covenant, the covenant of works. The oneness and the deity of the person are of importance for the affirmation that Christ could not sin (48).

The impeccability of Christ that stabilizes the covenant of grace in its immutability is not owing to the deification of his humanity, but from the fact that his humanity subsists in a divine person. The covenant of works did not possess such stability because it did not have the God-man as its mediator. So while the covenant of works could be broken, the covenant of grace is indestructible.

The practical import of all this is that the immutable and guaranteed nature of the covenant of grace is given a concrete and real ground in the person of Christ himself. We do not affirm the certainty of God’s covenant in the abstract, but on the basis of who Christ is as its Mediator and Surety. The promise of God in the covenant of grace to be our God and for us to be his people is as unbreakable as the unity of the two natures in the divine person of the Logos. His two natures would first have to be ripped apart before the threads of God’s promise could be unravelled. The covenant of grace, in which we find the complete forgiveness of ours sins and eschatological fellowship with the triune God forever, is founded upon nothing less than divine omnipotence. So in Christ we can be absolutely sure that all of God’s promises are, in fact, Yes and Amen.

[1] For Vos’ critique of Lutheran Christology with respect to the communication of attributes see pp. 65-74, esp. 70ff.

[2] Vos asks, “Is this one subject, this one person in the Mediator, a divine or a human person?” He answers, “This person is divine, and not human or divine-human. In order to be immediately convinced of this, one may take the following into consideration. In the Logos, a divine person, who is immutable, is present from eternity. If now there can be but one person in the Mediator, and the divine person cannot be eradicated or changed, then it is self-evident that this one person is the divine person of the Logos. One can only maintain the immutability of God if one holds to the deity of the person in the Mediator. The choice lies between two persons or one divine person” (42).

But what I found of particular interest was the implication he drew from the personal unity between the human nature and the Logos. But before disclosing that insight, it will help us to consider briefly what exactly he means by this.

Simply understood, the Logos is the divine person (see p. 50). It is the Logos who assumes a human nature into the unity of the person. The hypostatic union is not the union of two persons, one divine and one human, but the union of two natures in one divine person, in the Logos. Appealing to Junius, Thesis 27:16, Vos writes, “The divine assumes, the human is assumed—not so that from these two a sort of third is forged together, but the human nature, at the outset [anhypostasis or impersonal], was assumed by the Logos into the unity of the person, and thus made [enhypostasis or in-personal]” (43).

What follows from this union is that “one may no longer separate [Christ’s human nature] from his deity” (48). So when we worship and pray to Christ, we do not abstractly worship and pray to his divine nature, in exclusion of his human nature. Rather, our worship and prayers are directed concretely to his divine person, which has assumed a human nature. In other words, we worship and pray to the Word become flesh, the Logos enfleshed. Christ is venerated as the God-man, “possessing human nature in the unity of the person” (48). So Vos writes,

That Christ the Mediator may no longer be prayed to and worshiped exclusively as God, apart from his humanity. As the Word become flesh, He is the object of our worship. His human nature is personally united to Him; it is taken into his hypostasis; one may no longer separate it from His deity. Just as the Triune Being of God exists only as triune being, and we do not worship an abstract Godhead but the triune God, even so the Logos may not be venerated in His abstract deity but in his concrete personality, which is both God and man (48).

We are now in a position to understand the implication of all this for the Old Testament revelation. Vos goes on to say that “even before his incarnation, it was only possible to believe in Him as the one who would become flesh” (48). This is grounded in the eternal counsel of peace (or covenant of redemption), in which the Son assumed his role as Mediator and Surety of the covenant of grace (see pp. 1-4) “not as the Logos in the abstract, but as the Logos who would become flesh in time. He did this as Logos incarnandus [to be incarnate]…” (84). He was anointed in his person to be Mediator from eternity (p. 90).

So the revelation of the Logos in the Old Testament was never speculative or abstract. Instead, it was entirely concrete as it disclosed his person to be incarnate. You could say the Old Testament draws its significance and meaning from what was to come in Christ. (Note it does not obtain a new meaning with the coming of Christ, but always had Christ as its center and goal). Vos makes a similar point earlier in his Reformed Dogmatics regarding the three offices under the old covenant: “Now, we must not derive from their offices what Christ was, but must rather infer from Christ what their offices were. They were anointed because He would be anointed; He was not anointed because they had been” (11; see also p. 90).

We can now come to Vos’ implication for understanding the Old Testament:

[O]ne prays directly only to the Son as Mediator, since the humanity assumed in the unity of His person can no longer be separated from his person. It is for that reason that all revelation of the covenant of grace under the old dispensation had to point forward; that [which was] presented was not the Logos qua talis [as such], as Head of the covenant who had secured it from eternity, but always the Logos who over the course of the centuries was to come and was to become flesh (49).

Notice three things. First, the revelation of the old covenant was not concerned with the Logos in the abstract, but concretely in his work of redemption, which he would accomplish in his incarnation. Vos assumes here the redemptive focus of revelation, which is reflected in his mention of the covenant of grace. In his Biblical Theology, he writes, “Revelation is the interpretation of redemption” (6).

Second, the shadows of Christ in the Old Testament—such as the offices of prophet, priest and king, Adam and Israel as sons of God, the angel of the Lord, Joshua, Melchizedek, etc.—pointed forward to the Logos who was to become flesh. These old testament types were never to be speculated about, but through them, in action and power, the eternal Logos worked redemption for the people of God, in anticipation of his coming in the flesh to accomplish final, eschatological salvation.

Third, and implied from our first two points, the Old Testament revelation had to point forward. The anticipatory nature of the old covenant revelation was founded upon the coming incarnation of the Logos in history to work salvation. Through the types and shadows, the old covenant believers looked forward to the Logos enfleshed, the God-man. In fact, as Vos said earlier, the Christ could not be believed upon except as the One who would become flesh.