Jeremiah watched the decline of the people of God into rampant apostasy and hypocrisy. They only wanted God involved when an enemy army appeared on their borders. All other times, the people of Jerusalem and Judah rejected the 'Word of the LORD' - most notably the kings and Temple teachers.
Jeremiah repeatedly warned, pleaded and called God's people to turn again to the LORD their God, with all of the hearts and minds. He told of God's future work when the Law would no longer be a codified set of writings that could be legalistically abused to entrench power, but when God's Spirit would write His law on people's own hearts in a new covenant.
Eventually Jeremiah watched his beloved city (Jerusalem) and Solomon's great Temple be destroyed even as he was taken to Egypt to flee the destroyers. His distress at his prophecies becoming reality is clear in his writings.
Jeremiah was regularly referred to in the New Testament writings, and the writer to the Hebrews uses the prophecy of the new covenant (Jeremiah 31 - Hebrews 8) to great effect, showing how Christ's coming, teaching, death and resurrection ushered in the New Testament/Covenant, and Christ's outpouring of the Holy Spirit at Pentecost wrote the Law on the hearts of God's people.
That includes us. We must remember the danger of legalistic abuse of Old Testament Law - and be just as cautious of reducing God's Word to a "break in case of emergency" - as when an enemy army is on the doorstep, or the death of a loved one, or faith-shaking event when we only turn to God's Word out of fear.
Let us be those who turn to God's Word to find it wealth and wonder in the good days, and allow the LORD our God to write His law on our hearts by His Holy Spirit. As we read Scripture, this writing will grow in depth and power in our hearts, so when the Day comes when we really need to know how great our God is, and the firm foundation of His promises, we will know and be ready to stand.
It didn't end well for Jeremiah in this life - but he knew the promises of the LORD. May we have the strength to do the same.