Charles Spurgeon Commentary Jeremiah 9:5

"And they will deceive every one his neighbor, and will not speak the truth: they have taught their tongue to speak lies; they weary themselves to commit iniquity." — Jeremiah 9:5 (ASV)

What a sad state they were in! Their tongues spoke lies without any teaching; but they schooled their tongues until they were masters of the art of lying. They were D.D.s, doctors of dissembling; they understood the art thoroughly. They had taught their tongue to speak lies, and they had committed so much evil that they even tired themselves in doing it.