Calvin’s understanding of natural law (also known as the interior law) can be clearly appreciated in a series of passages of his Institutes, but especially in his Commentary to Romans 2:14-16. Verse 14 of this passage states that the gentiles by nature do what is established in the law and this makes that their natural disposition serve as a law for them. Calvin uses this verse to offer his own definition of natural law where he connects natural law with people’s natural disposition. Calvin argues that the Gentiles must have some rule of righteousness from there is no nation so lost to every thing human, that it does not keep within the limits of some laws. (2.14) This means the Gentiles have a disposition to create laws and regulations, an aspect that for Calvin it indicates that all nations possess at least a notion of justice and rectitude. Such a natural notion would be implanted by nature in the hearts of men. (2.14) For Calvin this implanted notion means all nations have a kind of law associated with the nature of the present life that contrasts with the written law grounded in God’s will. Natural law, therefore, should be broad in scope by being available for all people among the nations where it constitutes a light of righteousness supplying the role that played the written law for the Jewish. This use of natural law seems to be grounded in Calvin’s belief that the Fall did not eliminate the human ability to reason (although it was tainted by sin). Natural law, therefore, is a gift given to humanity by God and not something humanity has constructed.
Commenting verse 15 which states that the work of the law written in people’s hearts and affirm that people’s conscience accuses them if something is done wrong, Calvin highlights that this notion of righteousness which is imprinted in people’s heart as discrimination and judgment and this makes them to make a difference between justice and injustice, honesty and dishonesty. In this respect, the kind of law of nature (or natural law) imprinted in the human people will make able God to judge them, even the most secrets of human persons. Calvin connects here natural law with people’s conscience. Natural law offers some guidance to people regarding what is right a what is wrong. Natural law, therefore, offers a basic notion of human consciousness helping people to be aware of their actions and decisions, including the consequence of those.
Besides connecting natural law with moral natural disposition and people’s conscience, Calvin also tended to refer the idea of natural law with what we call “common-sense.” For Calvin natural law proceeds from God and is grounded in a divine order of the cosmos. For this reason, he connects natural law with certain elements of civil affairs associated to the present life (Institutes I.3.1). In this regard Calvin seems to connect natural law with the precepts found in the Second Table of the Law. Calvin emphasizes the idea of equity defining as “the goal and rule and end of all laws.” (Institutes 4.20.16). By incorporating equity in the laws of all nations, Calvin suggests that these civil laws can play a similar role than the written law played for the ancient Jewish people. Put it in a few words: Following Calvin, the second Table of the Law can be summarized as a calling to practice civil equity. By equaling natural law with equity, Calvin seems to suggest that natural law is the minimum set of moral precepts. In this way, the natural law implanted in people’s hearts allows them to gain some knowledge of the divine will such as the notion of justice and equity but in a limited and restricted way. The written law then clarifies what natural law dictates.
An important implication of Calvin’s discussion of natural law is how this one can be a way for Christians to be a living testimony in the church and in the society they live in, besides being a tool for non-Christian people such as rulers to encourage human flourishing. In this respect, Calvin’s apparent dualism that exists between the Kingdom of God which is associated with God’s will and the political affairs associated to the rules of the present world constitutes a misreading in light of Calvin’s reflections regarding the role of natural law. Instead of radicalizing both realms, Calvin offers instead a view where Christ governs both as Lord: the Kingdom of God which is spiritual and the present world which is natural. This two-fold perspective allows Calvin to defend the idea that Christs governs in the church in the natural world but also in the heavens as Lord of the everything. Considering this, the role of each Christian in the present life is still important for the society because there is still time to promote the values of the Kingdom of God such as equity, justice, and civil order from a creational and providential perspective. By being connected to the present life, natural law in Calvin’s view allows civil authorities to create laws that conform to divine will, even they might not know this. This is useful for creating laws which regulates basic aspects of morality such as the dignity of human being, the preservation of life, and the significance of promoting civil order in a society, for instance. Last but not least, another advantage is that natural law allows to develop a common moral framework to encourage dialogue between societies of different religious and cultural backgrounds since the precepts of natural law are valid for all persons.