"Deceit" so typified their environment that it prevented them from having much of a relationship with Yahweh. They did not know God ( Jeremiah 9:3), and they refused to know Him. Even while they devotedly studied deception ( Jeremiah 9:5), they refused to "know" Him.
The verb "yada", "know," denotes much more than intellectual knowledge but rather that deep intimate knowledge that follows on the personal commitment of one life to another, which is at its deepest in the commitment of a man to God. It actually means to become one with. The culture was one with evil not with good. This is why I say that we are living once again in the days of Jeremiah.
The tongue of this "daughter" was as deadly as an arrow (Jeremiah 9:3). Her words appeared to be peaceful, but she was really setting a trap for her neighbors. People greeted their neighbors amicably on the streets, but in their hearts they intended to harm them. The tongue can only bring up out of the heart what is in the heart. If we let people talk long enough we find out what is in them. God sees our hearts and knows the wickedness that dwells inside of us. Becoming one with God and living a life of obedience to Him purifies our heart.
Yahweh asked, rhetorically, if He should not punish such a nation for their deceits. His nation had become like all the other nations (Jeremiah 9:24-25). Should He not avenge Himself by punishing Judah for violating His covenant commands? The grief of God is caused not only by what the people have done to Him but by what they have done to each other. When we speak ill of one another it is like poisoness arrows directed into the person to assassinate them. Selfishness and pride can kill any people.
In verse thirteen Yahweh tells them the land will lay desolate. Instead the people had followed their own desires and the Baals, just like their ancestors. "Stubbornness" was one of their chief sins. "The threat of "stubbornness" still exists today. It has been described as "atrophy of the will". When people stubbornly refuse to do right, the time comes when they cannot do right. Judgment then comes in the form of living in the prison you have erected for yourself.
At the end of this chapter the Lord tells Jeremiah to hire mourners. People shouldn't take pride in neither their wisdom or their youth and that our only hope comes from our relationship with God. To me chapter 9 here of Jeremiah is so timely. We need to pray that our nation turn back to God especially during this election. Please exercise your right as an American citizen to vote and when you do--vote the Bible! our nation depends on it.