How is the Old Testament different from the New Testament?

from the old testament

• The Old Testament records the creation of the universe (Genesis 1), the first man and woman (Genesis 1:26–27, 2), and their sin, which brought all of creation into corruption and death (Genesis 3). As it does, God begins promising a Savior (Genesis 3:15) who would come through Abraham’s line and be a blessing to all nations (Genesis 12:3).
• In addition to the promise of a Savior, specific, national promises were given to Abraham, such as the promises of land (Genesis 15:18–21). Later, through David, Israel would also be promised an everlasting kingdom (2 Samuel 7:12–13).
• All of the promises, both salvific and national, were passed along to Isaac (Genesis 26:3–4) and Jacob (Genesis 28:13–14), who was later renamed Israel (Genesis 32:28). After Israel (Jacob) died, the Israelites were all in the land of Egypt and subsequently became enslaved there (Exodus 1:8–11). Moses was sent to rescue Israel from slavery to take them to their Promised Land (Exodus 3:10) and, through Him.
• After the Exodus and before they began traveling in earnest, God gave the Israelites the Mosaic Law (Exodus 19:3–6; Deuteronomy 5:1–3). Those laws governed Israel’s relationship with God and were never intended to be applied directly to believers today.
• Within the Law was the gift of the sacrificial system, so that the Israelites could restore their relationship with God after they sinned (Leviticus 17:11). However, those sacrifices were temporary solutions and had to be offered continuously. They pointed to the need for a once-for-all, permanent sacrifice.
• A Savior, known as the Messiah in the Old Testament, was promised as the final sacrifice (Isaiah 52-53). Within those promises included hints that such salvation would extend beyond the Jews to include the Gentiles (Isaiah 49:6), and involve an internal transformation rather than an external system of laws (Jeremiah 31:31–34).

from the new testament

• The New Testament opens with the arrival of the promised Messiah, Jesus (Matthew 1:1–23). He fulfilled the Mosaic Law (Matthew 5:17). Believers are no longer under that law but “under grace” (Romans 6:14), meaning they are saved on the basis of faith in Jesus, who is perfect, rather than in their own obedience (Ephesians 2:8–9).
• Unlike the Old Testament sacrifices, which had to be repeated, Jesus was the perfect Lamb. As the Son of God (John 20:31), He took on human flesh so that, in His perfect human nature, He was able to die for sin (Hebrews 2:14; Philippians 2:7–8). Since His human death fully satisfied human guilt, He needed to die only once (Hebrews 10:10). He now lives in heaven, offering forgiveness of sin and salvation through Him (Hebrews 7:25).
• After Jesus ascended back into heaven, He sent the Holy Spirit, who initiated the church (Acts 2:1–4). As a new and distinct entity from Israel, it had been hidden in the Old Testament, which is why Paul referred to it as a mystery (Ephesians 3:1–6). It is in the church that God extends his salvific promises to include Gentiles (Ephesians 2:14–16), so that both Jews and Gentiles are now saved in the same way: through Jesus (Acts 4:12).
• However, the church is not an extension of Israel, which remains a distinct entity in God’s plans. While salvation has expanded to all nations, God’s national promises have not. Right now there is a partial hardening of the Jews such that only a few are saved (Romans 11:25b), but in the future, after the time of the Gentiles is finished (Romans 11:25c), all of Israel will be saved (Romans 11:26) and reign as a distinct nation in Jerusalem, to which all other nations will come and offer gifts to its King, Jesus (cf. Zechariah 14:16). See Romans 9–11 for Paul’s full explanation for the purposes and distinctions between Gentiles and Israel.
• In addition to the Israel-Church distinction, another distinction is the work of the Holy Spirit. While He was active in the Old Testament, His role was largely external. However, He now directly indwells every believer (1 Corinthians 6:19), helping them obey God and grow to be more like Jesus (Galatians 5:16–24).

implications for today

All of Scripture is important for knowing who God is, who we are, who Jesus is, and how to be saved. That is why Paul, who included the Old Testament, said that all of Scripture is “profitable for teaching, for reproof, for correction, and for training in righteousness” (2 Timothy 3:16). We cannot fully grasp everything we need to understand about salvation and Christian living if we don’t have the Old Testament.

However, the Bible was not written as a single unit or “one testament” because they have differences. In the Old Testament, Jews were under the Mosaic Law, but now, in the New Testament era, we are no longer bound by those laws. Instead, our relationship with God is through Jesus. He kept the Law perfectly and died to pay for the sins of those who could not. Through His life, death, and resurrection, God made a way for us to be reconciled to Him (John 14:6). Therefore, the primary difference between the testaments is Jesus.

If you are currently striving to obey the Law as if that will save you, know that obeying it didn’t even save the Jews in the Old Testament! The Law was given to them as a tutor that revealed their need for a Savior (Galatians 3:24), but knowing the Law only increased their sin (Romans 5:20). This is because our sinful selves rebel against whatever we are told to do. The entire Scripture points towards Jesus. Have you turned to Him for salvation?