In Reformed theology, everything is built on Scripture alone–Sola Scriptura. We don’t build our theology on the New Testament by itself. The Old Testament is the bedrock and foundation for the New. As Paul said, our theology is built on the foundation of the apostles AND the prophets (Eph. 2:20). With this in mind, it’s important to remember the majority of Old Testament literature is about the Mosaic Covenant.
What was the Mosaic Covenant?
“It’s a law covenant with Israel, wherein God graciously leads them to Christ by showing them the perfect righteousness that only Christ could fulfill to redeem sinners.” ~ Sacred Bond.
In its narrow sense, the Mosaic covenant drove people to Christ for salvation. It demanded perfect obedience, just as the law given to Adam. In fact, the law given to Adam continued to be a perfect rule of righteousness; and, as such, was delivered by God upon Mount Sinai, in ten commandments (WCF 19.2).
God does not change and neither does His law. It’s unrelenting in its demands for perfect obedience and it’s unforgiving. In a sense, the Mosaic law is analogous to the covenant of works made with Adam. Israel received either curses or blessings based on their obedience to the law.
But while the Mosaic covenant was law driven in its narrow sense, in its wide sense it’s an administration of the covenant of grace. It continued and grew out of the promise made to Abraham. It didn’t cancel or replace it. It served the purpose of driving the people of Israel to Christ for salvation.
The Mosaic covenant was an outward administration of the one covenant of grace. Nothing about it changed God’s promises made to Abraham. It had rules and conditions that had to be followed. With obedience came blessings—long life in the promised land. With disobedience came curses—exile from the land (Deut 11:26-28).
Why was there a Mosaic Covenant?
If you ask most people where they will go when they die the majority would probably say “heaven.” If you asked them “why?” they’d probably answer “because I’m a good person.” Most people believe God grades on a curve, so they usually compare their goodness to the worst human beings who’ve ever lived.
The Mosaic covenant reminds us that the standard to meet God’s holiness is perfection. Leviticus 18:5 summarizes the Mosaic covenant: “Keep my statutes and my rules; if a person does them, he shall live.”
When the rich young ruler asked Jesus what to do for eternal life (Luke 18), Jesus told him to keep the Ten Commandments (Mosaic covenant). The disciples correctly understood the impossibility of salvation by works. It led them to ask “who can be saved?” Jesus told them, “What is impossible with man (covenant of works) is possible with God (covenant of grace).”
This passage demonstrates the primary use of the Law of God is to break us of our imagined self-righteousness and to drive us to seek our righteousness from Christ. It may have been one of many passages that led Paul to conclude that by works of the law no human being will be justified in his sight (Romans 3:20).
If Abraham “believed God, and it was counted to him as righteousness” why was the Mosaic Law even put in place? Paul answers that it was added because of transgressions, until the offspring (Jesus) should come to whom the promise had been made (Galatians 3:21).
Does this mean the Mosaic covenant is contrary to the covenant of grace? Paul answers Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe (Galatians 3:21-22).
Just to be clear, the Mosaic covenant was not a restoration of the covenant of works. Paul makes it clear that no one can keep the covenant of works and receive eternal life—that time passed with Adam.
Berkhof explains that the covenant of Sinai was not a renewal of the covenant of works, [but] in it the law was made subservient to the covenant of grace. The chief purpose of the Mosaic law was not to save Israel—it was not salvific. Its purpose was to be a tutor and drive people to Christ (Galatians 3:24).
Why is the Mosaic Covenant important for Christians?
Believers in Israel during the Mosaic time period were never saved by law keeping. It was impossible for Israel to earn eternal life by keeping the law. Believing Israelites were saved through faith alone in the mediator just as Christians are today, they just didn’t know His name. When Abraham “believed God, and it was counted to him as righteousness” he was partaking of the substance of the covenant of grace—Christ.
As Reformed Christians, we believe Jesus completed both an active and passive obedience on our behalf to the law of God.
Jesus’ active obedience refers to Him fulfilling the covenant of works in our place. His passive obedience refers to Jesus’ substitutionary atonement for us by dying on the cross. The Mosaic covenant provided the perfect landscape for both of these to take place.
Samuel Petto once wrote that “if [Jesus] had not been born under the very law, as a covenant of works, he should not have satisfied it.” This helps us to see the Mosaic covenant gave Jesus the picture-perfect situation for Him fulfill the covenant of works on our behalf. This is why Paul could say, “For as in Adam all die, so also in Christ shall all be made alive” (1 Cor 15:22). So, this is how the Mosaic covenant still helps us: it helps us remember in whom we are alive. It reminds Christians of our daily need for the gospel by driving us out of our self righteousness and causing us to rest in the righteousness of Christ!