As a practicing Christian, I decided to read the Bible in its entirety. If you’ve done this—or even if you haven’t—you’ll know that one of the greatest challenges is developing a working mental framework to understand the relationship between the Old and New Testaments. This was a challenge for the apostles as well (circumcision or no circumcision in the Book of Acts, for example). It even led to early church splits, such as when the Gnostics refused to reconcile the God of the Old Testament with Christ as one and the same.

In this post, I’m focusing specifically on the concept of the law as it appears in the Old and New Testaments—not the nature or actions of God across both, which is a much bigger undertaking. To better understand the relationship between the Old and New Testaments as it pertains to the law, I looked to the teachings of the early Church, the words of Jesus, and my Protestant faith.

Old Testament law can feel overwhelming when you first begin to read the Bible. Many of these laws clearly no longer bind Christians today. To clarify the various types of Old Testament law, I turned to St. Thomas Aquinas. Aquinas divided Old Testament law into three categories: moral, ceremonial, and judicial. Moral law is dictated by natural law; ceremonial law pertains to divine worship; and judicial law governs the justice maintained among people. Aquinas concluded that only moral law remains applicable to Christians.

The Ten Commandments are a clear example of moral law, while much of the Book of Leviticus provides examples of ceremonial and judicial law. For Christians, the law has been sharply reduced in light of Aquinas and early Church teaching. With that in mind, we can now turn to the New Testament—and specifically to the words of Jesus—to further understand the law’s place in the life of a believer.

In Matthew 5:17, Jesus directly addresses his relationship to Old Testament law:
“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.”
Clearly, the moral law is still applicable, but Jesus has fulfilled the law perfectly on our behalf.

Later in Matthew (22:34), the Pharisees tried to trap Jesus with a question:
“Teacher, which is the greatest commandment in the Law?”
Jesus replied:
“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.”

This is a powerful quote and speaks directly to the relationship between Old Testament law and Christian living. It also provides a practical guide for how we, as Christians, should approach daily life and relationships. Jesus simplified the law down to its core message. First: love the Lord your God with all your heart, soul, and mind—a daunting task! We must seek the Lord daily through His Word and prayer. In a world full of distractions, this is no easy feat, but daily seeking is a strong starting point.

Second: love your neighbor as yourself. This often feels more approachable, but can still be difficult—especially when dealing with someone who is hard to love. In these moments, we must remember that all people are made in the image of God (Genesis 1:27). I also believe that these two commandments clearly point us toward genuine Christian service, especially to those in difficult or less fortunate circumstances.

My Protestant faith has further developed my understanding of the law (again, referring to moral law only). The law serves as a mirror to reveal our sin (Romans 3:20). It helps us recognize our sin—something made easier by the fact that the law is written on our hearts (Jeremiah 31:33; Romans 2:15). When we love the Lord our God with all our heart, soul, and mind, we become more aware of our sin. And through prayer and the power of the Holy Spirit, we strive to avoid sin, even while knowing we’ll never be completely sinless.

As Christians, we hold onto the truth that Jesus fulfilled the law, but we also acknowledge that the law continues to reveal our sin and drive us to repentance.

In closing, I want to quote Dietrich Bonhoeffer at length to further clarify the daily struggle of Christian life:
“Every day Christ’s followers must acknowledge and bewail their guilt. Living as they do in fellowship with Him, they ought to be sinless, but in practice their life is marred daily with all manner of unbelief, sloth in prayer, lack of body discipline, self-indulgence of every kind, envy, hatred and ambition.”
(Bonhoeffer, The Cost of Discipleship)

As Christians, we will continue to fight the daily battle. But we live in hope, because we know that Christ has already won that battle for us—and that all the law and the prophets ultimately come down to this: seeking Him with all our heart, soul, and mind, and loving our neighbor as ourselves.