John Calvin Commentary Jeremiah 38:24

"Then said Zedekiah unto Jeremiah, Let no man know of these words, and thou shalt not die." — Jeremiah 38:24 (ASV)

Here we see the miserable condition of the king. If he had no faith in Jeremiah's answer, he would not have feared so much. But he acknowledged that what he had heard from the Prophet's mouth was true. Meanwhile, he delayed and extended time as far as he could, and chose rather to spend his life trembling than to be immediately freed from all care and anxiety.

This was by no means acting like a king, for if he had any courage, he would not have waited until the last hour. Indeed, we know that men of courage boldly meet death when they see no hope of honor remaining. Zedekiah had lost his authority. He indeed held the title of a king, but he was without power, for he was compelled to obey his counselors servilely. Now he feared his own shadow and yet, as I have said, he prolonged time as much as he could. For this reason, he requested the Prophet that this conversation might remain buried.

By saying, you shall not die, he was not threatening the Prophet, but intimating that silence would be no less a benefit to Jeremiah than to himself: “You will rouse the fury of all against yourself if you speak of this interview, for no one can bear to hear anything about the ruin of the city. If then you consider your own benefit, do not say a word about this, and do not let it reach the people or my counselors.” Under the guise of advice, then, he said to Jeremiah, “Take care, lest you die.” Therefore, he was not speaking threateningly.