Sermon Text: Jeremiah 31:31-34
Date: October 26, 2025
Event: Reformation Day, Year C

Jeremiah 31:31-34 (EHV)

Yes, the days are coming, declares the LORD,
when I will make a new covenant with the house of Israel
and with the house of Judah.
32It will not be like the covenant I made with their fathers,
when I took them by the hand
and led them out of the land of Egypt.
They broke that covenant of mine,
although I was a husband to them, declares the LORD.
33But this is the covenant I will make with the house of Israel after those days,
declares the LORD.
I will put my law in their minds,
and I will write it on their hearts.
I will be their God,
and they will be my people.
34No longer will each one teach his neighbor,
or each one teach his brother, saying, “Know the LORD,”
because they will all know me,
from the least of them to the greatest, declares the LORD,
for I will forgive their guilt,
and I will remember their sins no more.

The LORD Reforms Us

When do you need reform? Activist groups may call for reform in some area of leadership or government when they sense that the plans and actions of those in charge are not in line with the leadership’s stated goals—or the desires of the people involved. You may sense a need for reform in your own life when bad habits start pushing out good habits, and you find yourself not dedicated to your priorities and values like you want to be. Reform may be called for when a group’s actions or policies reflect a different era. These ways of doing things may have made sense in the past, but perhaps that reasoning no longer applies today.

A commonality among all of these different types of reform is that it’s going to be work. It’s going to be uncomfortable. It’s going to be difficult. Trying to steer the ship of an organization from the bottom up when those from the top disagree is a gargantuan task. Implementing new plans and goals that are different from the standard, traditional path someone has been following for a long time can be incredibly taxing. And I don’t need to tell you how tough it is to fight against your own ingrained habits to make long-lasting, meaningful changes in your day-to-day life.

All reform is uncomfortable because it’s tackling the status quo and trying to change it; it’s a fight against inertia, and sometimes it feels like trying to roll a boulder up a steep hill.

As we observe and celebrate the 508th anniversary of the beginning of the Lutheran Reformation this morning, we thank God for all the blessings he brought to the church through Martin Luther and the other reformers many years ago that we still benefit from today. But we also do well to recognize that this reformation work in the 1500s was not unique to that time; this is work that God had been doing and will continue to do among his people as long as this world endures.

There are many periods of reformation within Bible history that we could point to, but our focus this morning is the work of the prophet Jeremiah. Jeremiah’s ministry was often pretty bleak. He ministered among an unfaithful nation-church as he served as a prophet to the nation of Judah. The leaders and the people of Judah were often unfaithful to God’s direction and teaching. In fact, Judah was already a splinter nation from the formerly great nation of Israel. After the days of King Solomon, that nation broke into two pieces. The northern piece was also unfaithful (perhaps even more thoroughly than Judah) and met their end through sweeping exile by the nation of Assyria some 150 years before the days of Jeremiah.

But Judah’s unfaithfulness was very real, and though the nation was rescued from the consequences of their unfaithfulness at the hands of Assyria, it ended up just being a delay rather than a complete rescue. Eventually, God had to step in to force a true reform that the people were not doing themselves. He did this, in part, through the exile of the people of Judah by the nation of Babylon.

It's at this time of unfaithfulness and consequences to that unfaithfulness that Jeremiah served. He had the unenviable task of warning the people that the nation’s destruction and people’s exile were coming. There would be no miraculous rescue from Babylon had there been from Assyria 150 years earlier.

God describes his people’s unfaithfulness to him here in Jeremiah and elsewhere using the terms of a marriage that has fallen to pieces. The people’s unfaithfulness was spiritual adultery against their loving husband. When God says, “They broke that covenant of mine,” he uses the terms of annulment and divorce. The people’s unfaithfulness to God’s covenant sought to end the spiritual, eternal marriage of God to his people.

It would be easy to imagine that the Babylonian captivity would be God’s version of giving his wife a certificate of divorce and sending her away. But this is reform, not abandonment. Yes, Jerusalem would be pulverized by Nebuchadnezzar, the Babylonian king. Yes, God’s people would be ripped out of their homeland and sent marching across the Fertile Crescent to Babylon. But this was not God divorcing his adulterous wife and sending her away; this was part of God’s reform of his Old Testament church.

God promised that seventy years after the exile, they would return. And in many ways, this reform “worked.” After the Babylonian exile, we don’t really see God’s people struggling with the worship of false gods like Baal, Asherah, and Molech. Instead, there is a newfound commitment to the truth of God’s Word and prioritizing it in the lives of God’s people.

But this reform is not just a story of getting a people group to straighten up and fly right. That would ignore the reality of sin and imply that God was having the people fend for themselves and even save themselves. Instead, ahead of the exile, God promises something different, something new, through Jeremiah: Yes, the days are coming, declares the LORD, when I will make a new covenant with the house of Israel and with the house of Judah. It will not be like the covenant I made with their fathers.

The “old” covenant that God made with the nation of Israel when he brought them out of Egypt was an earthly-blessing-focused covenant. God would be their God and bless them. He would give them the Promised Land as an enduring gift on the condition that they were faithful to him. Their job was to obey God; God’s job was to provide for them.

Obviously, we know how that went. But here God is promising something new and different. Instead of the old covenant promised and given primarily through Moses, this new covenant would be entirely God’s doing. It would be radically different in that it wouldn’t involve any work from the people at all. God was making and keeping this promise completely independent of anyone else. But this is the covenant I will make with the house of Israel after those days, declares the LORD. I will put my law in their minds, and I will write it on their hearts. I will be their God, and they will be my people.

The word translated “law” here in v. 33 is probably best understood as the whole of God’s Word. God is not simply promising to put his commands into the people’s hearts. In many ways, that was already true as all people are born with a natural knowledge of God and with that have a conscience that testifies to God’s will—what things are right and what things are wrong. No, this is something bigger, broader, something God will have to inscribe on the hearts of his people. This heart-writing will include the gospel; it will include God’s grace—his undeserved love—for his people. This reform would be centered not on God’s justice, but on his mercy, his forgiveness. No longer will each one teach his neighbor, or each one teach his brother, saying, “Know the LORD,” because they will all know me, from the least of them to the greatest, declares the LORD, for I will forgive their guilt, and I will remember their sins no more.

This forgiveness—so potent that it makes the all-knowing God forget!—would be carried out by a descendant of the people facing exile. Almost 600 years after Jeremiah, the time will fully come, and God will send his Son, Jesus, into this world. God himself would take on our human nature, our flesh and blood, to live and die as our substitute. In the blood of Jesus shed at the cross, atonement—payment for sin—would be made to cover our sins and reunite us with our God.

God would reform the Israelites to be faithful, but more than that, they would be reformed to be forgiven. The faithful among this nation would put their trust in God as their eternal Savior and giver of eternal life. The forgiveness and even the faith to trust it would be a one-sided action on God’s part. Our obedience—a life of sanctification, of good works—is purely a thankful response to God’s freely-given grace and forgiveness.

The church of Martin Luther’s day was unfaithful to God’s covenant in a similar way to Old Testament Judah. The papacy and the church in Rome at large had distorted God’s Word to such a point as to rob all the comfort God intended the people to have. The message of sins fully and freely forgiven in Jesus’ death was absent, replaced with a message of works. If you wanted to receive actual forgiveness for your sins, the church said, you needed to do something to compensate for it. Maybe that was prayers, maybe that was some works of service. Perhaps that was paying the church money so they would tell you you were forgiven.

None of this is what God said, so through Luther and others, God restored the true teaching of his Word. While reform never really came for the Roman church (as it still holds to this works-righteousness teaching even today), it did come for Christendom at large. All over the western world, God worked a change so that the people would hear and know what he had done, the new covenant he had established, a covenant that did not call for works from us, but is a one-sided covenant that depends entirely on God’s undeserved love for us.

We need God’s reform. We need him to correct our hearts and actions. We need him to redirect our gaze away from ourselves and back to him. We need him to show us our great need for rescue and that we have that rescue freely given in Jesus’ work for us.

Thanks be to God! He has written these truths on your heart and mine through his Word and sacraments. By God’s grace, we don’t have to encourage each other to learn about—to know—the God of free and faithful grace. He has made himself known to us and even dwells within us. And the promise made through Jeremiah, the promise reinforced at the time of the reformation, is the promise that rings true for you and me today: I will forgive their guilt, and I will remember their sins no more.

My brothers and sisters, so complete is your forgiveness that God can’t even remember that you’ve ever been unfaithful to him or sinned against him. Our sins are gone, completely wiped out in the blood of Jesus shed for us. So let us live our lives in a way that reflects the reformation that God has worked in each of us. Let us give thanks to God our Savior in everything we say, think, and do—now and forever! Amen.

Soli Deo Gloria