One account of morality sees history as the outworking of a competition between groups that are vying for power. Another account grounds morality in personal preference or choice. In contrast to these accounts, the historic Christian faith affirms a revealed standard of morality that is grounded in the divine Creator Himself.
The Basis of Natural Law
While this morality is most clearly revealed in the special revelation of Scripture, the created order and human conscience also bear witness to the same ground of morality. God’s invisible attributes are clearly perceived in the things that have been made (Rom. 1:20). A law is also “written on the heart” (2:15). According to this view, these external (nature) and internal (conscience) witnesses to the Creator’s moral standard render all people “without excuse” (1:20). This universal and accessible law is also called the natural law.
The natural law has been the bedrock of western moral and political thought for centuries. It is built upon two assumptions. First, there is an order to nature—that nature conforms to a law and isn’t chaotic. The Lord God created “plants yielding seed, and fruit trees bearing fruit in which is their seed, each according to its kind” (Gen. 1:11). A maple seed is directed toward its inherent end to become a maple tree and produce more maple seeds. This purpose is not willed upon it by mankind but built into its nature. Second, human beings are rational creatures that can discover this order, which is binding on everyone; the Lord endued men and women with “reasonable” souls (WLC Q. 17).
The natural law is distinct from positive or civil laws that are enacted and enforced by legislators. It is also categorically distinct (though, of course, not separated) from God’s eternal decree. However, the natural law is not autonomous. Herman Bavinck discussed the natural law under the topic of God’s general revelation, where he writes, “This revelation of God is general, perceptible as such, and intelligible to every human. Nature and history are the book of God’s omnipotence and wisdom, his goodness and justice.” Elsewhere, he holds together the books of general and special revelation: “It is one and the same God who in general revelation does not leave himself without a witness to anyone and who in special revelation makes himself knows as a God of grace.”
A fundamental aspect of the natural law is whether nature has an intrinsic aim, or telos. Unfortunately, more modern uses of the natural law assume a mechanistic understanding of nature. For example, Kant’s categorical imperative provides the basis for moral action on the sovereignty of the will. Nature no longer witnesses to morality; instead, nature becomes something to manipulate and master for our own ends. The manipulation of nature for our own ends is demonstrated in the topic of homosexuality.
What does the natural law teach us about sexuality? The answer is found by returning to God’s original purposes for making man “male and female.” This duality does not assume that one is unequal or inferior. Instead, it upholds the dignity of male and female because society can only arise from the sexual difference of each. Thus, sexuality aims toward generation. The blessing of God upon Adam and Eve serves the purpose of forming a family: “Be fruitful and multiply and fill the earth” (Gen. 1:28).
While sexuality aims for this good, it does not mean that it always actualizes this good. A husband and a wife may not be able to actualize this good for several reasons. But the aim remains in their sexuality even without its actualization. Not all acorns grow into oak trees, but the potential is still present in each acorn. In contrast, generation is inherently impossible between two persons of the same sex. In short, disordered sexuality doesn’t even have the potential for generation.
This aim of sexuality requires a second good, which is unity, commitment, or faithfulness. The reason we find so many commands in Scripture that uphold marriage and family, such as honoring your parents (Ex. 20:12), keeping the marriage bed undefiled (Heb. 13:4), and being faithful to your spouse (Eph. 5:22–33), is that the stable union between a husband and a wife is good for society. The friendship that begins with a man and a woman forms the basic building block for society.
This kind of friendship between a husband and a wife is different than a friendship between two men. We observe bonding among men in various settings, which serve the good aims of encouragement and admonishment toward virtuous living. “Iron sharpens iron, and one man sharpens another” (Prov. 27:17). But this kind of friendship is incompatible with the sexual friendship between a husband and wife. It cannot be a sexual friendship because it does not have the potential to fulfill the sexual good of generation. To pretend otherwise is to lie about the created order and the aim of the sexual difference between male and female.
Let me conclude with three points of application. First, recovering the natural law provides a firm foundation as we witness to non-Christians; namely, the foundation of creation. Bavinck writes, “As a result of this general revelation, they feel at home in the world; it is God’s fatherly hand from which they receive all things also in the context of nature. In that general revelation, moreover, Christians have a firm foundation on which they can meet all non-Christians.” Thus, the biblical condemnation of sodomy and homosexuality is grounded first in the natural law as a witness to God’s created order.
Second, these two goods of sexuality—procreation and union—require the commitments of marriage and family life. We must exhort faithfulness between a husband and a wife, admonish wickedness such as pornography and adultery, and strengthen laws that protect marriage, such as getting rid of no-fault divorce law. Protecting and supporting marriage and the family demonstrates an interest in society. Relaxing these laws leads to disorder because it goes against the natural witness of the divine Creator.
Third, the issue at the heart of the topic of sexuality is the issue of authority. The natural law is that it reminds us that we are not our own and do not make ourselves. As C.S. Lewis writes in The Abolition of Man, “For the wise men of old”—who recognized that they were but creatures—“the cardinal problem had been how to conform the soul to reality, and the solution had been knowledge, self-discipline, and virtue.” Conforming the soul to reality, which is essential to knowing our place in the created order, includes our conforming of our thoughts, words, and deeds—all of which are in rebellion against the divine Creator. It necessitates the disciplines of chastity or faithfulness in marriage.
Ultimately, this reality to which the created order witnesses is the Lord God Almighty, who is not just the Maker of heaven and earth, but also our Redeemer. For while the natural law witnesses to the Creator, it is insufficient to save. Rather, God’s special revelation of the good news of Jesus Christ is the only hope for a creation, and people, that longs for restoration. Only the saving grace of Jesus Christ received by faith provides eternal salvation and freedom from our sins. Only the saving grace of Jesus can redeem the entire person with the promise of eternal life and the hope of the Holy Spirit to walk in newness of life now. Only the saving grace of Jesus can restore God’s creation to its rightful aims, including the most natural of all societies—the family, beginning with man and woman.
 Reformed Dogmatics, 1:310.
 Reformed Dogmatics, 1:322.
 Reformed Dogmatics, 1:321.