Reformed theology teaches and the Reformed Churches confess that the Old and New Testaments are fundamentally unified in important ways. The triune God of the New Testament is the God of the Old Testament. The Apostle John says that God the Son, the Word, who became incarnate (John 1:14) is the person of the Holy Trinity through whom all things came into being and without whom nothing was created (John 1:1–3). Another way to express this unity is to say that there is one covenant of grace with multiple administrations. The covenant of grace that was revealed and began to be externally administered in redemptive history after the fall, in the promise by God of the Seed of the Woman who was to crush the head of the serpent and whose heel would be stricken by the serpent (Gen 3:15). The covenant of grace was progressively revealed more clearly through redemptive history in the promise of salvation to and through the Noahic covenant (Gen 6:18), and again through Abraham (Gen 12:1–3), that God would bless all the nations of the earth through him (Acts 2:39b), that God would give him a seed that would number more than the stars in the sky (Gen 15:5, 6), and finally in Genesis 17:7, “And I will establish my covenant between me and you and your offspring after you throughout their generations for an everlasting covenant, to be God to you and to your offspring after you,” which the prophets and apostles paraphrased and repeated repeatedly through Scripture (e.g., Jer 32:38–41; Joel 2:28–32; Acts 2:39). The Lord said that he gave the land to the Israelites not because of their obedience but because of his gracious covenant he made with Abraham (Deut 9:5). God was gracious to Israel because of his gracious covenant with Abraham (2 Kings 13:23). The Apostles invoked the covenant of grace in their explanation of redemptive history (Acts 3:25; 7:8). Against the Judaizers, the Apostle Paul explicitly contrasted the Abrahamic covenant of grace as prior to and more fundamental than the Mosaic covenant (Gal 3:15–29). To the Roman congregation he argued that we are Abraham’s children (Rom 4[all]).

In light of all this, it is no wonder that the Reformed Churches confess that there is essentially one covenant of grace throughout redemptive history that is variously administered, under types and shadows under the Old Testament and openly in the New Testament. According to the Reformed understanding of Scripture the covenant of grace was not merely revealed under the types and shadows but rather it was substantially present in, with, and under the types and shadows. The New Covenant is the covenant of grace without the types and shadows but it is the present administration of the covenant of grace that has been present in salvation history since Genesis 3:15.

The Reformed Confessions

Belgic Confession (1561)

For that reason we detest the error of the Anabaptists who are not content with a single baptism once received and also condemn the baptism of the children of believers. We believe our children ought to be baptized and sealed with the sign of the covenant, as little children were circumcised in Israel on the basis of the same promises made to our children. And truly, Christ has shed his blood no less for washing the little children of believers than he did for adults. Therefore they ought to receive the sign and sacrament of what Christ has done for them, just as the Lord commanded in the law that by offering a lamb for them the sacrament of the suffering and death of Christ would be granted them shortly after their birth. This was the sacrament of Jesus Christ.

According to Reformed theology, the ground of infant baptism is God’s promise to Abraham. They are entitled to participate in the external administration of the one covenant of grace as it is administered in under the New Covenant as covenant children were entitled to receive the sign of admission to the visible covenant community under the types and shadows.¹*

heidelberg catechism

74. Are infants also to be baptized?

Yes, for since they belong to the covenant and people of God as well as their parents, and since redemption from sin through the blood of Christ, and the Holy Spirit who works faith, are promised to them no less than to their parents, they are also by Baptism, as the sign of the Covenant, to be ingrafted into the Christian Church, and distinguished from the children of unbelievers, as was done in the Old Testament by Circumcision, in place of which in the New Testament Baptism is instituted.

The churches of the German Palatinate repeated this approach in the Heidelberg Catechism. Notice how the Reformed Churches appeal to the “sign of the covenant” instituted under the Old Testament (i.e., Abraham) to inform New Covenant practice.

second helvetic confession (1566)

And since there is always but one God, and there is one mediator between God and men, Jesus the Messiah, and one Shepherd of the whole flock, one Head of this body, and, to conclude, one Spirit, one salvation, one faith, one Testament or covenant, it necessarily follows that there is only one Church (ch. 17).

The Second Swiss Confession, written by Heinrich Bullinger c. 1561, at the request of Frederick III, Elector Palatinate,  explicitly confessed “one faith, one testament or covenant” and thus “one church.” This is the same argument that Bullinger had been making since 1534 (De testamento), which Zwingli had been making against the Anabaptists since 1523.

canons of dort

Since we are to judge of the will of God from His Word, which testifies that the children of believers are holy, not by nature, but in virtue of the covenant of grace, in which they together with the parents are comprehended, godly parents ought not to doubt the election and salvation of their children whom it pleases God to call out of this life in their infancy (Canons of Dort, 1.17).

In their response to the Remonstrants, who alleged that the Reformed theology condemned infants to hell, the Reformed Churches of the Netherlands, France (in absentia), the British Isles, Geneva, et al. appealed to the unity of the covenant of grace to explain their doctrine that believers whose children die in infancy trust that such children are with the Lord.

westminster confession of faith

7.4. This covenant of grace is frequently set forth in Scripture by the name of a testament, in reference to the death of Jesus Christ the Testator, and to the everlasting inheritance, with all things belonging to it, therein bequeathed.

7.5. This covenant was differently administered in the time of the law, and in the time of the gospel: under the law, it was administered by promises, prophecies, sacrifices, circumcision, the paschal lamb, and other types and ordinances delivered to the people of the Jews, all foresignifying Christ to come; which were, for that time, sufficient and efficacious, through the operation of the Spirit, to instruct and build up the elect in faith in the promised Messiah, by whom they had full remission of sins, and eternal salvation; and is called the old testament.

27.5. The sacraments of the old testament, in regard of the spiritual things thereby signified and exhibited, were, for substance, the same with those of the new.

The Westminster Divines explicitly confessed multiple administrations of “[t]his covenant.” When the divines spoke of “the law’ and “the gospel” in in this context, they were using the traditional historical distinction between the Old and New Covenants. The divines were not saying that Moses is only law theologically or that the New Testament is only gospel theologically but were merely using the language used by the church since Irenaeus (c. AD 170).

helvetic consensus formula (1675)

Canon XXIV: But this later Covenant of Grace according to the diversity of times has also different dispensations. For when the Apostle speaks of the dispensation of the fullness of times, that is, the administration of the last time (Eph 1:10), he very clearly indicates that there had been another dispensation and administration until the times which the Father appointed. Yet in the dispensation of the Covenant of Grace the elect have not been saved in any other way than by the Angel of his presence (Isa 63:9), the Lamb slain from the foundation of the world (Rev 13:8), Christ Jesus, through the knowledge of that just Servant and faith in him and in the Father and his Spirit. For Christ is the same yesterday, today, and forever (Heb 13:8). And by His grace we believe that we are saved in the same manner as the Fathers also were saved, and in both Testaments these statutes remain unchanged: “Blessed are all they that put their trust in Him,” (the Son) (Ps 2:12); “He that believes in Him is not condemned, but he that does not believe is condemned already” (John 3:18). “You believe in God,” even the Father, “believe also in me” (John 14:1). But if, moreover, the holy Fathers believed in Christ as their God, it follows that they also believed in the Holy Spirit, without whom no one can call Jesus Lord. Truly there are so many clearer exhibitions of this faith of the Fathers and of the necessity of such faith in either Covenant, that they can not escape any one unless one wills it. But though this saving knowledge of Christ and the Holy Trinity was necessarily derived, according to the dispensation of that time, both from the promise and from shadows and figures and mysteries, with greater difficulty than in the NT. Yet it was a true knowledge, and, in proportion to the measure of divine Revelation, it was sufficient to procure salvation and peace of conscience for the elect, by the help of God’s grace.

Written by J. H. Heidegger and Francis Turretin against the Amyraldians and others and adopted by the Swiss Reformed Churches until the first quarter of the 18th century, the Swiss Consensus reflected the broad and deep Reformed agreement that there is one covenant of grace, which is administered (dispensed) variously throughout redemptive history. Notice how they were at pains to stress the unity of salvation, that the church, under both testaments, were saved by grace alone, through faith alone. The covenant of grace was present in, with, and under the types and shadows and revealed more fully under the New Covenant.

Resources

1. How To Subscribe To Heidelmedia
2. Calvin On The Unity Of The Covenant Of Grace
3. More From Calvin On The Unity Of The Covenant Of Grace
4. Ursinus: Christ Was The Author And Mediator Of The Old Covenant
5. Turretin: We Affirm The Unity Of The Covenant Of Grace Against The Socinians, Remonstrants, And Anabaptists
6. Witsius: One Covenant Of Grace, Multiple Administrations
7. Brakel: The Substance Of The Covenant Of Grace Is Identical In The Old And New Testaments
8. Bavinck: The Reformers Taught One Covenant Of Grace In Two Administrations Against The Anabaptists
9. Vos: The Substance Of The One Covenant Of Grace Was In The Old Covenant
10. Vos: The Covenant Of Grace Was Present In, With, And Through The Old Testament Types And Shadows
11. Jude On The Continuity Of The Covenant Of Grace
12. The Abrahamic Covenant Unifies Redemptive History
13. What Is The Substance Of The Covenant Of Grace?
14. The Substance and Administration of the Covenant of Grace
15. Covenant Theology & Infant Baptism
16. Tracing The Paradigm Shift: Two Ways Of Being In The Covenant Of Grace
17. A Brief History Of Covenant Theology
18. “A House of Cards? A Response to Bingham, Cribben, and Caughey,” in Matthew Bingham, Chris Caughey, R. Scott Clark, Crawford Gribben, and D. G. Hart, On Being Reformed: Debates Over a Theological Identity (London: Palgrave-Pivot, 2018), 69–89.

NOTES

1. Theodore Beza, in his 1560 Confession, wrote:

This definition pertains to the sacraments of the old as well as to the new covenant and shows the difference between them.
First, those of the ancient covenant or alliance were ordained only until the coming of Jesus Christ (1 Cor. 10:4); but these of the new alliance are established until the consummation and end of the world (Heb. 12:27).
The second difference of the sacraments of the ancient alliance directed the faithful to Jesus Christ who was to come; but these of the new alliance direct us to Jesus Christ already come (1 Cor. 10:2–4; Augustine, Three books against the Letters of Petilian, Bk. 2, 37.87; “Tractate 26.12” and “Tractate 45.9,” on John). The third difference is in the signs and ceremonies which differ greatly (Augustine, Letter to Januarius, 54.1; Christian Doctrine, Bk. 3, 9.13). The fourth is in the number of them and in the measure of their signification. For, as St. Augustine says, we now have fewer sacraments than our elders, easier and of better signification, and as a consequence of much greater efficacy and power. Here are all the differences which we find. And to conclude, the one and the other proceed and come only from one author, i.e., from the goodness of God only (Heb. 1:1); and they both tend to no other end but to make man a partaker of Jesus Christ, to enjoy eternal life, as St. Paul declares (1 Cor. 10:2–4; Rom. 4:11) and St. Augustine (“Tractate 26.12,” on John). (ch. 32)

We do not cease to communicate baptism to young children even though their faith is unknown to us. We have said before that it is requisite that they should be partakers of the fruits of the sacraments (Acts 8:36–37). And it is not very likely that they have faith because they do not have the use of understanding (Deut. 1:39; Rom. 10:14, 17), except God works in them extraordinarily (which does not appear to us).
First, there is now the same reason for baptism which was once in circumcision (called by St. Paul “the seal of righteousness which is by faith,” Rom. 4:11), even the express commandment of God by which the male children were marked the eighth day (Gen. 17:12).
Second, there is a special regard to be had to the infants of believers, for although they do not have faith in effect such as those do who are of age, yet they have the seed and the spring in virtue of the promise which was received and apprehended by their elders. For God promises not only to be our God if we believe in Him, but also that He will be the God of our offspring and seed; yes, to the thousandth degree, i.e., to the last end (Ex. 20:6). Then by what right or title do they refuse to give them the mark and ratification of what they have and profess already? And if they allege further that although they come from faithful elders or parents, does it not follow that they are of the number of the elect and as a consequence that they are sanctified (for God has not chosen all the children of Abraham and Isaac, Rom. 9:6–8), the answer is easy. It is true, all those are not of the kingdom of God who are born from believing parents, but with good right we leave this secret to God to judge who alone knows it (2 Tim. 2:19). Nevertheless, we justly presume to be the children of God all those who are the issue and descended from believing parents according to the promise (Gen. 17:7; 1 Cor. 7:14). For it does not appear to be the contrary to us. Accordingly, we baptize the young children of believers, as has been done from the time of the apostles in the church of God (Origen, Commentary on Romans) and we do not doubt that God by this mark (joined with the prayers of the church, their assistants) seals adoption and election in those whom He has eternally predestined, whether they die before the age of discretion or whether they live to bring forth the fruits of their faith in due time, and according to the means which God has ordained (ch. 48).

James T. Dennison Jr., Reformed Confessions of the 16th and 17th Centuries in English Translation: 1523–1693, vol. 2 (Grand Rapids, MI: Reformation Heritage Books, 2008–2014), 284–285, 293–94.