The prophet Jeremiah preached after the destruction of the Kingdom of Israel and during the reigns of Jehoiakim, Jeconiah, and Zedekiah as kings of Judah. Although during his time as a prophet he suffered persecution from the ruling class of his country, his reread texts left a profound legacy in the Israelites exiled in Babylon, and the book of the prophet, is the testimony of how a nation falls due to the lack of the spiritual gift of fear of God (constancy, firmness, devotion).
His book begins with a call from God to the prophet, who was chosen from the womb by the divine providence, and a prophecy about the destruction of the kingdom of Judah at the hands of an enemy from the north; although this mysterious enemy is not named later in the book it is identified as the Babylonian Empire. And the prophet then in his book relates how the Israelites had lost fidelity to the word of God and had given themselves over to idolatry.
In those times, because of the hardness of hearts, the King and the most important priests only wanted to hear pretty lies, and Jeremiah's warnings had become a great nuisance. Like every prophet, Jeremiah reminded to the israelites that there are behaviors ordered to rewards and behaviors ordered to punishments, as explained in Psalm 1, the Psalm of the two paths, and that when men lose the common sense that is born from the gift of fear of God, beyond any human calculation the destructive unforeseen events arrive: "I will lay stumbling blocks before this people; fathers and son alike will be staggered; friends and neighbors will perish" Jeremiah 6:21.
The prophet had been chosen by God as the examiner of his people, and so the prophet in one of his oracles sentenced how the ignorance of the wisdom of God is the origin of sin, and so he affirmed with intelligence about this problem: "They progress from one evil to another, and they don't know me" Jeremiah 9:3. As the prophet taught, hardness of heart, which is the rejection of grace and his word, can only bring misfortune, the opposite of that heart of flesh that fears God.