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How the Old Testament Informs an Ethic that is Thoroughly Christian

The application of the Old Testament to the Christian today is a source of much discussion. Murmurs of “legalism” and “not earning salvation” seem to arise anytime the “Law or the Prophets” are discussed (Matt 5:17). Yet such accusations blur the glory of God’s Word, functionally diminish—even if giving lip service to inerrancy—the influence of nearly three-quarters of the Bible, and hamstring both the need for unbelievers to be saved and for believers to grow in Christlikeness (2 Tim 3:14-17; Rom 8:28-30; ESV).[1] In this essay, I make the case that the Old Testament is both necessary and beneficial in developing an ethic that is thoroughly Christian. I will make this argument in three steps. Jesus’s view of the law and the prophets from Matthew 5:17-20 will be used to give the foundation for why the Old Testament is significant in developing a thoroughly Christian ethic. Second, I will articulate how the Old Testament informs a Christian ethic specifically. Third, I will provide uses of this ethic for Jesus’s followers today.


It takes a whole Bible to make a whole Christian. Ethics and morality are rooted in the eternal law of God. The Old Testament displays God’s character and His eternal plan of redemption that helps make sense of the New Testament. The Old Testament displays the tension caused by humanity’s covenantal failures with God and thus their desperate need to be reconciled to His “very good” design. This eternal story climaxes in God taking on human flesh in the person of Jesus Christ. Thus, in the words of A.W. Tozer, “Nothing less than a whole Bible can make a whole Christian.”

Matthew 5:17-20. Critical to understanding the continuity and discontinuity spectrum between the Old and New Testaments are Jesus’s words in Matthew 5:17-20:

Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished. Therefore whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever does them and teaches them will be called great in the kingdom of heaven. For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven.

A proper understanding of what Jesus meant to “fulfill” the “Law or the Prophets” is necessary to interpret the Old Testament in light of the New. The law was divided into three parts for ancient Israel: (1) the civil law, (2) the ceremonial law, and (3) the moral law. Jesus fulfilled the civil (or judicial) law—a temporary safeguard providing consequences for those who disobeyed the moral law (e.g., Exod 21:15; Deut 22:8)—as the One who is both “just and the justifier of the one who has faith” in Him (Rom 3:26). Jesus fulfilled the ceremonial law—revolving around the sacrificial offerings to atone for sin and restore a right relationship with God—by both observing this law and becoming the sacrificial atonement for sin (John 1:29, 36; 1 Cor 5:7; Col 2:16–17; Heb 9:11-28, 10:1–10). Jesus fulfilled the moral law—articulated by the Ten Commandments (Exod 19:1-17)—by living a life of perfect obedience to God the Father (2 Cor 5:21). While parts of the law that related to ethnic Israel are now obsolete, the moral law—rooted in the eternal law of God—will remain forever (Matt 5:17-18; Mark 7:19; Acts 10:9–16). Jesus fulfilled the “Law” and “the Prophets.” Yet not one iota or dot has passed or will ever pass from the eternal law of God. These laws provided a two-dimensional line drawing for Israel of God’s eternal character that Jesus fills in with living and vibrant color as the image of the invisible God (John 1:18; Col 1:15). While there are aspects of the “line drawing” that can no longer be seen, the image is unmistakable. Thus, grave consequences and glorious rewards are assigned to those who denigrate or propagate the intent of the “least of these commandments” (Matt 5:19).

Under Grace. A proper understanding of what it means to be “under grace” is necessary to alleviate the perceived tension between Paul’s words “not under law but under grace” and Christ’s warning that “unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven” (Matt 5:20; Rom 6:14; 10:4; Gal 5:18). The Old Testament alleviates this perceived tension. Ezekiel prophecies about the day when God will put His own Spirit within someone and “cause” them “to walk in my statues and be careful to obey my rules” (Ezek 36:27). Jeremiah also prophecies, “I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people” (Jer 31:33). On this subject, Jonathan Pennington writes, “as with the Beatitudes, the priority of internal disposition over external purity is the vital issue.”[2] This “righteousness” far “exceeds” that of the religious elite tangibly because the eternal law of God is not a dutiful burden applied externally but a means of inner delight within the heart. While Christ’s imputed righteousness is necessary for anyone to be born again, the righteousness that is in view here refers to a holistic righteousness that manifests itself in visible ways as the result of having been “born again” (John 3:3). Paul himself writes to the Corinthians that he is “not free from God’s law but am under Christ’s law” and calls the Galatians to “fulfill the law of Christ” (1 Cor 9:21; Gal 6:2). Tom Schreiner summarizes, “Theologically, what we find here fits with what is called the law of Christ in Paul. The law is fulfilled in Christ and must be interpreted in light of Christ’s coming. Hence, the focus is no longer on the law but on Christ himself.”[3]


Having identified why the Old Testament is necessary, this section will identify how the Old Testament informs a Christian ethic in three specific areas.

1 - The Genesis Blueprint. The first two chapters of God’s Word provide a sense of order, purpose, and beauty inherit in His creation. Genesis 1 and 2 are referred to as the “Genesis blueprint.” This blueprint provides humanity with God’s “very good” design. The first two chapters of Genesis answer the fundamental questions of life: who we are as people made in God’s image, where we came from, and what our sense of purpose is (Gen 1:26-28).

2 - Sexual ethic. The Genesis blueprint also provides humanity with God’s sexual ethic that has endured for millennia upon millennia as that which is true, good, and beautiful. While the word “good” is repeated twelve times in the first two chapters of Genesis, God sees that it was “very good” after creating male and female (Gen 1:4, 10, 12, 18, 21, 25, 31; 2:9, 12, 15, 17, 18). Genesis 1-2 presents God’s “very good” design for sexual ethics: (1) one man and one woman (2) united in a one flesh union (3) for a lifetime. God uses this union to display His relationship with humanity. God brings forth children from the complementary and intimate union of a husband and wife knowing each other as naked and unashamed (Gen 2:25). This union is the means by which humanity is to “Be fruitful and multiply and fill the earth” (Gen 1:28). The beauty of God’s sexual ethic is confirmed by Jesus, the apostles, and Paul (Gen 1:28; 2:23-25; Matt 5:27-28; 19:3-9; Mark 7:21; 10:2-10; Acts 15:28-29; 1 Cor 6:9-11, 13-20; Eph 5:22-23). This biblical sexual ethic is also vindicated by modern day statistics that show the deteriorating effects of sexuality that reject the Genesis blueprint.[4] The Genesis blueprint has significant implications on ethical issues such as artificial reproductive technologies, in vitro fertilization (IVF), surrogacy, contraception, birth control, abortion, homosexuality, the transgender movement, etc..

3 - Ten Commandments. The Ten Commandments provide God’s moral standard for all people across all time. God has written this moral standard both on tables of stone and on all people’s hearts (Eccl 3:11; Rom 2:14-15). David Jones writes, “As a revelation of God’s character, the moral law is timeless, unchanging, and the standard by which God judges’ man.”[5] Thus, moral law does not begin with the Decalogue. The Decalogue simply identifies for humanity the moral law that exists in the eternal law of God. Christians recognize, however, that this standard is merely a starting point for a higher moral standard—the eternal law of God that is manifested in God Incarnate, Jesus Christ. The New Testament repeats the Decalogue with the implication that the moral code to which it points to is still in effect (Matt 5:21, 27; 19:17–19; Mark 10:19; Luke 18:20; Rom 7:7; 13:9; Eph 6:2–3; and Jas 2:11.47). Jesus articulates this higher standard in His Sermon on the Mount (e.g. “you have heard that it was said, but I say to you …; Matt 5:21, 27, 31, 33, 38, 43). Paul notes that the “law is good, if one uses it lawfully” (1 Tim 1:8). No one is or ever has been saved by keeping the moral law (Rom 3:10-11). At the same time, those who are saved “by grace” are drawn to Christ’s higher moral standard (Eph 2:8; Matt 5:20). Jesus did not just fulfill the law. He is the very embodiment of the eternal law. The three forms of law are an essential “shadow of the things that were to come” that point to the “reality … found in Christ” (Col 2:17). To be “born again” changes one’s posture from “what can I get away with” to “how can I be restored to and best enjoy God’s ‘very good’ design?” One cannot negate the broader standard of the law and then uphold the higher standard for which this law points. Understood properly, the pursuit of holiness is not a burdensome duty but becomes one’s greatest delight. In this way, “Holiness turns out to be our greatest joy.”[6]


There are three areas where this ethic is immensely important for Christians to embrace. First, the moral law as found in the Old Testament is insightful for evangelism and apologetics.

Evangelism and apologetics. Every unbeliever is living a life that is less than the “very good” design that God created them for. God has written His moral code on both tablets of stone and stony hearts (Exod 20:1-17, 34:1; Deut 6:22; Rom 2:14-15). Perhaps there is no more powerful “gospel bridge” than to appeal to the moral code that God has already written on the unbeliever’s heart (Rom 2:14-15). Unbelievers have to know that they are lost and that they are suppressing the truth (Rom 1:18). The moral law helps them recognize their lostness. It provides a broad road map towards fulfillment. The Old Testament speaks to the condition of the human heart like no other work in history. Thus, the Old Testament has immense value in evangelism.

Salvation (conversion and sanctification). The Old Testament has soteriological value for both conversion and sanctification. Paul reminds Timothy of the scriptures that were able to make him “wise for salvation through faith in Christ Jesus” (2 Tim 3:15). God uses the Old Testament to “mortify sin and vivify the Spirit.”[7] Paul writes to Timothy that “All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work” (2 Tim 3:16-17). Reading the Old Testament in light of Christ’s first coming causes a Christian’s affections for Christ to grow. It heightens the sense of need and the glory of God’s salvation. In so doing, the believer lives out God’s plan for salvation by becoming more and more like the One they worship (Rom 8:29-30; 1 Cor 15:48-49; 2 Cor 3:18; Phil 3:21; 1 John 3:2).

Societal. Finally, the Old Testament—particularly the Ten Commandments—provides a framework for the laws regulating society. In reference to the Decalogue prohibition of murder, Andrew Walker states, “we think all of society should abide by this … this is binding on all of humanity” (Exod 20:13).[8] The same could be said for commandments five through ten of the Decalogue. The Old Testament is particularly helpful because it is regulative and thus policeable by its very nature.


The Old Testament provides substantial insight into the eternal law of God. Jesus affirmed its importance for His followers (Matt 5:17-20). The Old Testament also has profound implications for the “abundant life” for which these followers were designed (e.g., purpose, sexuality, rest). Thus, it is essential in the development of an ethic that is thoroughly Christian. God is glorified when we enjoy life according to His good design. The Old Testament provides a necessary “shadow” that is recognized both on a societal level and also within the chambers of every human heart. Christians can use this “shadow” to point the “reality,” calling those who are weary and heavy laden to Christ, that they might learn from Him and “find rest for … [their] souls” (Matt 11:28-30).

[1] All Bible references are from the English Standard Version unless otherwise noted. [2]Jonathan T Pennington, The Sermon on the Mount and Human Flourishing: A Theological Commentary (Baker Academic, 2017), 179. [3] Thomas R. Schreiner, 40 Questions About Christians and Biblical Law (Grand Rapids, Mich: Kregel Publications, 2010), 162. [4]“‘Gay Marriage’ and Distant Consequences: Homosexuality, Sexual Immorality and the Downfall of American Civilization » Americans for Truth,” accessed January 15, 2022, as well as Mark Regnerus, “How Different Are the Adult Children of Parents Who Have Same-Sex Relationships?,” Social Science Research, Findings from the New Family Structures Study, 41, no. 4 (July 2012): 752. [5]David W. Jones, An Introduction to Biblical Ethics, ed. Daniel R. Heimbach, B&H Studies in Biblical Ethics (Nashville, Tennessee: B&H Academic, 2013), 60. [6]Zane Pratt, “Spiritual Warfare in Evangelism and Missions: Lectures” (Lecture, Spiritual Warfare Lectures, Southern Seminary (Zoom Meeting), December 2020). [7]Andrew Walker, “Survey of Christian Ethics” (Lectures, The Southern Baptist Theological Seminary, January 2022). [8]Walker, “Christian Ethics: Lecture.”


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