Why will the Lord put his law in his people and write it on their hearts?

Faced with the incurable unfaithfulness of his people, the only hope is the Lord’s willingness to make a new covenant. It is striking to notice that the basis of the original covenant was not the law given at Mt Sinai, but rather the fact that the Lord took them by the hand to bring them out of the land of Egypt (Jeremiah 31:32). The original covenant was based on the Lord’s grace and his willingness to powerfully save his people. The new covenant would be based on the same grace. This new covenant will be made after those days, that is, after the Lord has rescued his people.¹ However, this time the Lord’s grace would go even further. But this is the covenant that I will make with the house of Israel after those days, declares the Lord: I will put my law within them, and I will write it on their hearts. What the Lord says through Moses in Deuteronomy 30:1–20 and Deuteronomy 31:1–30 when he renewed his covenant with the generation that was about to enter the land, is very important background to this promise to write the law on their hearts in Jeremiah 31:33.² In Deuteronomy, the law was given through Moses as a written document that was to be stored in the Ark of the covenant as a witness against the nation (Deuteronomy 31:24–26). But the written law was also to be a living document that must be read by the people and taught to their children (Deuteronomy 31:9–13; Deuteronomy 6:4–9). For the people of Israel, the law was not too hard for you, neither is it far off. It is not in heaven, that you should say, Who will ascend to heaven for us and bring it to us, that we may hear and do it? Neither is it beyond the sea, that you should say, Who will go over the sea for us and bring it to us, that we may hear it and do it? But the word is very near you. It is in your mouth and in your heart, so that you can do it. (Deuteronomy 30:11–14). As they lived in the land, they had the law with them all the time, not just in their mouths, but they could even take it to heart. The terms of the covenant were always for the people to love the Lord your God with all your heart and with all your soul and with all your might as they lived in obedience to his law (Deuteronomy 6:5). The reality, however, is that with the original covenant, the law was only ever written in a book. Even though it meant that Israel had the law right there with them on a daily basis, the law as a written document was not enough to overcome their hard hearts. Jeremiah refers to this hardness of heart in his book as the reason for covenant failure (Jeremiah 13:10;Jeremiah 17:1;Jeremiah 23:17). Under this new covenant, this vital barrier to the success of the covenant would be overcome as the Lord himself would write his law on the very hearts of his people, not in a document via a mediator as in the old covenant. Incredibly, this barrier of hard, rebellious hearts was anticipated even in the old covenant (Deuteronomy 29:1–29) and so even the old covenant looked forward to the Lord’s promise to overcome the unfaithful hearts of his covenant people (Deuteronomy 30:1–10). The promise in Jeremiah 31:33 makes it clear that the time for that promise to be fulfilled has begun.

It should be noted that there is both continuity and discontinuity between the old and the new covenants.³ As with the old covenant, the new one will mean that the Lord will be their God, and they shall be my people. This relationship will also be based on the Lord’s saving grace toward his people and the people’s wholehearted love for the Lord, and for their neighbour. The law will still form the basis of what this love for the Lord and for the neighbour looks like. However, the big difference under the new covenant is that the Lord would do an internal spiritual work in his people that transforms their hearts and brings about the loving obedience of the Lord that the old covenant describes. This obedience from the heart would go beyond just external law keeping and would express the full intention of the law as a description of the good life.