Traditionally, the formal origin of covenant theology is back to Cocceius. However, elements of the covenant theology can be found in the whole Scriptures in a broad sense. The notion and language of covenant, grace, works, and promise was well known by the early Church and Catholic theologians before Reformation. Passages such as Gen. 3:15, Rom. 11, Deut. 29;1, and Hos. 6:7, show such language, for example. Nonetheless, properly speaking, the theology of covenant as we know it today has its origin in the larger development of the sixteenth-century Reformation.
Zwingli, contemporary of Luther, is known for defending the continuity of the Old and New Covenant and arguing that the rite of circumcision was replaced by Christian baptism. For him, baptism was the initiation ritual to the Christian community. These two claims were not isolated in Zwingli’s theology, but it was part of his understanding of the covenant. For Zwingli, the covenant seems to be bilateral and conditional. But at the end, it is God who unifies the covenant through Jesus Christ. In a nutshell, Zwingli introduced the notion of covenant in early Reformation connecting the baptism as a sign of the covenant among God’s people.
Bullinger was the first reformed theologian to write an entire treatise about the covenant titled “De testamento.” Despite this achievement, his understanding of the covenant follows Zwingli in many respects. For him, the covenant between God and humanity seems to be bilateral since it involves both parties (God and humanity), although humanity did not decide to start it but God. It this God’s desire to be in covenant with humanity what starts the covenant. The covenant seems to be also conditional because humanity has some conditions and responsibilities to fulfill. Humanity needs to be obedient to be able to fulfill the covenant. Despite his apparent bilateral and conditional dimension, the covenant is one, where the different ‘covenants’ God has celebrated with human figures such as Adam, Noah, Moses, David, for instance, are manifestations of the same covenant of grace. This made that the covenant, for Bullinger, has a progressive character. Last but not least, another important feature Bullinger highlights is the continuity of the covenant since Adam until us. The covenant, for him, has never been interrupted despite Adam’s failure.
Unlike Zwingli and Bullinger, Calvin seems to defend a unilateral dimension of the covenant of grace. Although it has been controversial, Calvin clings to both, the covenant of works and the covenant of grace. But since he developed more the discussion of the covenant of grace, the idea that he also supported the notion of a covenant of works still stirs some controversy among theologians. In order to appreciate this, however, one must reject the hermeneutic promoted by the old school that hold a radical tension between Calvin and the Calvinists. The first feature of Calvin’s notion of the covenant is that seems to speak of a covenant of works, but in an implicit way. Calvin’s discussion of the covenant of works cannot be seen as crystal clear as his discussion of the covenant of grace. This fact, however, does not discard the idea. In this respect, Calvin speaks of certain law that Adam had to follow, and that is the divine command of not to eat from the forbidden tree. But Calvin sees other elements besides this prohibition. He also identifies the parties involved, sees a promise, and a punishment. The second feature is that, for Calvin, the notion of a covenant of work seems to be rooted in the obedience of the moral or natural law. For him, Adam needed to follow the natural law. And last, Calvin believes there is one single unilateral covenant of grace, speaking in a broad sense. He claims that in a broad sense the mosaic covenant and the gospel (new covenant) are indeed one. However, he also recognizes that in a narrow sense, the gospel is unconditional, unlike the mosaic law that was conditional. In summary, Calvin seems to stress strongly the notion of grace in both in the covenant of works and in the covenant of grace, having into account that for Calvin, the terms ‘testament’ and ‘covenant’ were, in many ways, interchangeable.
Musculus, a second-generation reformed theologian, also contributed to the development of the theology of covenant in the early Reformed church. Like other reformed theologians, Musculus discussed the notion of the covenant in his theology. Although he believed in two covenants, he believed that the first covenant was general intended for the whole humanity. The second covenant was special intended only for believers. With this innovation, Musculus seems to differ from the position his fellow reformed theologians had developed around the language and content of the covenants. However, it is not the purpose of this exam to debate Musculus’s understanding of the covenant and how much he differed from his predecessors.
Finally, Ursinus and Olevianus, also offered a good consolidation of the reformed theology of the covenant. Ursinus emphasized the God-humankind relationship and argued that the covenant of creation (or covenant of nature) had the purpose of creating a way to obtain life as reward of obedience and blessings. By means of the covenant of creation, God entered into a covenant with humanity, where they had to obey God’s commandments. Ursinus deduced the covenant of creation from the Genesis narrative and his connection with the doctrine of the Image of God, and natural law (implanted in humankind). Because Adam and Eve couldn’t fulfill the covenant and failed in obtaining the blessings promised, then Christ’s role had to fulfill the covenant of creation by his complete submission to God for the benefit of believers. In this way, because Christ bore the curse of the covenant of creation, he entered into the covenant of grace with believers fulfilling God’s promise. As seen, for Ursinus, the covenant is just one where God’s promise of grace is given to the elect or believers. Similar to Ursinus, Olevianus made significant contribution to the reformed theology of covenant starting with a refined development of the covenant of grace. He seemed to stress the bilateral dimension of the covenant. But, the covenant of grace must be understood in a twofold sense: a broad and narrow sense. In the broad sense, the covenant of grace covers all people baptized in the name of Christ. This would include all Christians from difference groups, adults, children, and so on. Now, the covenant of grace in its broad sense only has basic coverage. Because of this, the narrow sense of the covenant of grace is of high importance since it includes both benefits – the justification and sanctification of the elect. The believers receive those benefits by faith.
In conclusion, something that Zwingli, Bullinger, Calvin, Musculus, Ursinus, and Olevianus had in common was their interest in studying the covenant theology. In their time, each of these theologians laid some kinds of foundations to the reformed doctrine of the covenant. As one observes, some of them such as Zwingli and Bullinger seem to be in contrast with Calvin’s view of the covenant. Nonetheless, such tension is apparent (except if one adopts the position of the old school that defended a strong tension between federal and predestinarian theologians). Recent scholarship (Mueller, Bierma, etc.) has developed and noted the apparent contradictory views of the covenant were not a sign of complete disagreements or opposing theologies, but a just a difference of emphases (or dimensions) made by early Reformed theologians.