If Christians are part of the new covenant, why should we seek to understand and apply the Old Testament (OT)? I’ll give 10 reasons why the first word in the phrase Old Testament must not mean unimportant or insignificant to Christians.

1. The OT was Jesus’s only Scripture and makes up three-fourths (75.55 percent) of our Bible.

If space says anything, the OT matters to God, who gave us his Word in a book. In fact, it was his first special revelation, which set a foundation for the fulfillment we find in Jesus in the New Testament (NT). The OT was the only Bible of Jesus and the earliest church (e.g., Matt. 5:17Luke 24:44Acts 24:142 Tim. 3:15), and it’s a major part of our Scriptures.

2. The OT substantially influences our understanding of key biblical teachings.

By the end of the Law (Genesis–Deuteronomy), the Bible has already described or alluded to all five of the major covenants that guide Scripture’s plot structure (Adamic-Noahic, Abrahamic, Mosaic, Davidic, and new). The rest of the OT then builds on this portrait in detail. Accordingly, the OT narrative builds anticipation for a better king, a blessed people, and a broader land. The OT creates the problem and includes promises that the NT answers and fulfills. We need the OT to understand fully God’s work in history.

Further, some doctrines of Scripture are best understood only from the OT. For example, is there a more worldview-shaping passage than Genesis 1:1–2:3? Where else can we go other than the OT to rightly understand sacred space and the temple? Is there a more explicit declaration of YHWH’s incomparability than Isaiah 40, or a more succinct expression of substitutionary atonement than Isaiah 53? Where should we go to know what Paul means by “psalms, hymns, and spiritual songs” (Eph. 5:19Col. 3:16)?

Finally, the NT worldview and teachings are built on the framework supplied in the OT. In the NT we find literally hundreds of OT quotations, allusions, and echoes, none of which we’ll fully grasp apart from saturating ourselves in Jesus’s Bible.

3. We meet the same God in both Testaments.

Note how the book of Hebrews begins: “Long ago, at many times and in many ways, God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son” (Heb. 1:1–2). The very God who spoke through the OT prophets speaks through Jesus.

Perhaps the most foundational OT statement of YHWH’s character and action is Exodus 34:6: “The LORD, the LORD, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness.” The OT then reasserts this truth numerous times in order to clarify why it is that God continued to pardon and preserve a wayward people:

God’s grace fills the OT, just as it does the NT. Further, in the NT, Jesus speaks about hell more than anyone else. He declares, “Do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell” (Matt. 10:28). Thus, God is just as wrathful in the NT as he is in the OT.

Certainly there are numerous expressions of YHWH’s righteous anger in the OT, just as there are massive manifestations of blood-bought mercy in the NT. What is important is to recognize that we meet the same God in the OT as we do in the New. In the whole Bible we meet a God who is faithful to his promises to both bless and curse. He takes sin and repentance seriously, and so should we.

4. The OT announces the very ‘good news/gospel’ we enjoy.

The gospel is the good news that through Jesus––the divine, crucified, and resurrected Messiah––God reigns over all and saves and satisfies believing sinners. Paul states that “the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, ‘In you shall all the nations be blessed’” (Gal. 3:8, emphasis added). Abraham was already aware of the message of global salvation we now enjoy. Similarly, in the opening of Romans, Paul stresses that the Lord “promised beforehand through his prophets in the holy Scriptures” (i.e., the OT prophets) the powerful “gospel of God . . . concerning the Son” that he preached and in which we now rest (Rom. 1:1–3, 16).

Foremost among these prophets was Isaiah, who anticipated the day when YHWH’s royal servant (the Messiah) and the many servants identified with him would herald comforting “good news” to the poor and broken––news that the saving God reigns through his anointed royal deliverer (Isa. 61:1; cf. 40:9–11; 52:7–10; Luke 4:16–21). Reading the OT, therefore, is one of God’s given ways for us to better grasp and delight in the gospel (see also Heb. 4:2).

5. Both the old and new covenants call for love, and we can learn much about love from the OT.

Within the old covenant, love was what the Lord called Israel to do (Deut. 6:5; 10:19); all the other commandments simply clarified how to do it. This was part of Jesus’s point when he stressed that all the OT hangs on the call to love God and neighbor: “You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the great and first commandment. And a second is like it: You shall love your neighbor as yourself. On these two commandments depend all the Law and the Prophets” (Matt. 22:37–40). Reading the Old Testament is one of God’s given ways for us to better grasp and delight in the gospel.

Christ emphasized, “Whatever you wish that others would do to you, do also to them, for this is the Law and the Prophets” (7:12). Similarly, Paul noted, “The whole law is fulfilled in one word: ‘You shall love your neighbor as yourself’” (Gal. 5:14; cf. Rom. 13:8, 10). As with Israel, the Lord calls Christians to lives characterized by love. However, he now gives all members of the new covenant the ability to do what he commands. As Moses himself asserted, the very reason God promised to circumcise hearts in the new covenant age was “so that you will love the LORD your God with all your heart and with all your soul” (Deut. 30:6). Moses also said that those enjoying this divine work in this future day would “obey the voice of the LORD and keep all his commandments that I command you today” (30:8). Moses’s old covenant law called for life-encompassing love, and Christians today, looking through the lens of Christ, can gain clarity from the OT on the wide-ranging effect of love in all of life.

6. Jesus came not to destroy the Law and the Prophets but to fulfill them.

Far from setting aside the OT, Jesus stressed that he came to fulfill it, and in the process he highlighted the lasting relevance of the OT’s teaching for Christians:

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. (Matt. 5:17–19)

It’s important to note here that, while the age of the old covenant has come to an end (Rom. 6:14–151 Cor. 9:20–21Gal. 5:18; cf. Luke 16:16), the OT itself maintains lasting relevance for us in the way it displays the character of God (e.g., Rom. 7:12), points to the excellencies of Christ, and portrays for us the scope of love in all its facets (Matt. 22:37–40). As Moses asserted, in the day of heart circumcision (Deut. 30:6), which we are enjoying today (Rom. 2:29), all of his teachings in Deuteronomy would still matter: “And you shall again obey the voice of the LORD and keep all his commandments that I command you today” (Deut. 30:8).

7. Jesus said that all the OT points to him.

After his first encounter with Jesus, Philip announced to Nathaniel: “We have found him of whom Moses in the Law and also the prophet wrote” (John 1:45). Do you want to see and savor Jesus as much as you can? We find him in the OT. As Jesus himself said, “You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me” (John 5:39; cf. 5:46–47). “And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself” (Luke 24:27). After his resurrection, proclaiming the gospel of God’s kingdom (Acts 1:3), Jesus opened the minds of his disciples “to understand the Scriptures, and said to them, ‘Thus it is written that the Christ should suffer and on the third day rise from the dead, and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem’” (Luke 24:53).

A proper “understanding” of the OT will lead one to hear in it a message of the Messiah and the mission his life would generate. Similarly, Paul taught “nothing but what the prophets and Moses said would come to pass: that the Christ must suffer and that, by being the first to rise from the dead, he would proclaim light both to our people and to the Gentiles” (Acts 26:22–23). As an OT preacher, he could declare: “I decided to know nothing among you except Jesus Christ and him crucified” (1 Cor. 2:2). If you want to know Jesus more, read the OT!

8. Failing to declare ‘the whole counsel of God’ can put us in danger before the Lord.

Paul was a herald of the good news of God’s kingdom in Christ (e.g., Acts 19:8; 20:25; 28:30–31), which he preached from the Law of Moses and the Prophets––the OT (28:23; cf. 26:22–23). In Acts 20:26–27 he testifies to the Ephesian elders, “I am innocent of the blood of all, for I did not shrink from declaring to you the whole counsel of God.” The “whole counsel of God” refers to the entirety of God’s purposes in salvation-history as revealed in Scripture. Had the apostle failed to make known the Lord’s redemptive plan of blessing overcoming curse in the person of Jesus, he would have stood accountable before God for any future doctrinal or moral error that the Ephesian church carried out (cf. Ezek. 33:1–6Acts 18:6).

The Old Testament, while not written to Christians, was still written for us. With the NT the Scripture is complete, and we now have in whole “the faith that was once for all delivered to the saints” (Jude 3). This “faith,” however, is only understood rightly within the framework of “the whole counsel of God.” So may we be people who guard ourselves from blood guilt by making much of the OT in relation to Christ.

9. The NT authors stressed that God gave the OT for Christians.

Peter asserted of the OT prophets, “It was revealed to them that they were serving not themselves but you” (1 Pet. 1:12). The OT authors understood that they were writing for a future audience––Christians identified with the NT church.

Similarly, Paul was convinced that the divinely inspired OT authors wrote for NT believers, living on this side of the death and resurrection of Christ. “For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope” (Rom. 15:4; cf. 4:23–24). “Now these things happened to [the Israelites] as an example, but they were written down for our instruction, on whom the end of the ages has come” (1 Cor. 10:11).

Accordingly, the apostle emphasized to Timothy, who was raised on the OT by his Jewish mother and grandmother (Acts 16:12 Tim. 1:5), that the “sacred writings” of his upbringing “are able to make you wise for salvation through faith in Christ Jesus” (2 Tim. 3:15). People today can get saved from God’s wrath and from the enslavement of sin by reading the OT through the lens of Christ.

People today can get saved from God’s wrath and from the enslavement of sin by reading the Old Testament through the lens of Christ. This is why Paul says in the next verse, “All Scripture is . . . profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be competent, equipped for every good work” (3:16–17). New covenant believers can correct and reprove straying brothers and sisters from the OT, when read in relation to Christ, for in it we find many “profitable” things (Acts 20:20)––a “gospel of the grace of God” (20:24)––that call for “repentance toward God” and “faith in our Lord Jesus Messiah” (20:21).

Based on this fact, NT authors regularly used the OT as the basis for Christian exhortation, assuming its relevance for Christians (e.g., 1 Cor. 9:8–12Eph. 6:2–31 Tim. 5:181 Peter 1:14–16). Because we are now part of the new covenant and not the old, there are natural questions that arise regarding how exactly the Christian should relate to specific old covenant instruction. Nevertheless, the point stands that the OT, while not written to Christians, was still written for us.

10. Paul commands church leaders to preach the OT.

The last of my 10 reasons why the OT still matters for Christians builds on the fact that Paul was referring to the OT when he spoke of the “sacred writings” that are able to make a person “wise for salvation” and the “Scripture” that is “breathed out by God and profitable” (2 Tim. 3:15–16). Knowing this colors our understanding of his following charge to Timothy:

Preach the word; be ready in season and out of season; reprove, rebuke, and exhort, with complete patience and teaching. For the time is coming when people will not endure sound teaching but having itching ears they will accumulate for the themselves teachers to suit their own passion, and will turn away from listening to the truth and wander off into myths. (2 Tim. 4:2–4)

For Paul, Christian preachers like Timothy needed to preach the OT in order to guard the church from apostasy. While we now have the NT, we can, and indeed must, appropriate the OT like Jesus and his apostles did for the good of God’s church. Paul stresses that those who unhitch themselves from the OT put themselves in danger of falling away from God.