In this study of Jeremiah chapter four, we look at the fact that religion (even reformed religion) brings death.
"'If you, Israel, will return, then return to me,' declares the Lord. 'If you put your detestable idols out of my sight and no longer go astray, and if in a truthful, just and righteous way you swear "As surely as the Lord lives," then the nations will invoke blessings by him and in him they will boast.'" NIV translation
In chapter three, the prophet began to remind the people of what had happened to the northern kingdom. He shared the fact that God had called them to repent but they had refused and dug in their heels like a stubborn calf. The phrase "the nations will invoke blessings by him" refers to the fact that God had promised Abraham that God would make him a blessing (see Genesis 12). This is a reminder that Israel was to be a bright shining light in the dark pagan world.
"This is what the Lord says to the people of Judah and to Jerusalem: 'Break up your unplowed ground and do not sow among thorns. Circumcise yourself to the Lord, circumcise your hearts, you people of Judah and inhabitants of Jerusalem, or my wrath will flare up and burn like fire because of the evil you have done - burn with no one to quench it.'" NIV translation
Under King Josiah, there was a reformation as he instituted changes to draw people back closer to God.
Here, we see that this religious reformation did not begin with a changed heart. The "unplowed ground" speaks of the fact that there was no change of heart and so there could be no repentance.
The word circumcise literally means "to cut around" and the people were willing to have their children circumcised but it was not a cutting of the heart. A cutting of the heart is a sorrow at sin and its effects. Without that change of heart, the reformation was simply a tweaking of behavior.
"'Announce in Judah and proclaim in Jerusalem and say: "Sound the trumpet throughout the land!" Cry aloud and say: "Gather together! Let us flee to the fortified cities! Raise the signal to go to Zion! Flee for safety without delay! For I am bringing disaster from the north even terrible destruction.'" NIV translation
Now, we see that this reformation of religion without the revival of the heart will bring death. The prophet announces the coming judgment on the kingdom of Judah and tells them that Babylon is going to be the nation that God uses.