John Calvin Reformed @genevareformer

Now the Prophet tells us that he was sent to the king and his counsellors. Hitherto he has been addressing the king and the whole people indiscriminately; but here a special message is committed to him to be delivered at the palace of the king; and he was to say that judgment was nigh him and his counsellors.

Matthew Henry Presbyterian @wholebiblehenry

By the civil message which the king sent to Jeremiah it appeared that both he and the people began to have a respect for him, which it would have been Jeremiah's policy to make some advantage of for himself; but the reply which God obliges him to make is enough to crush the little respect they begin to have for him, and to exasperate them against him more than ever.

Commenting on Jeremiah 21:8-14

John Gill Reformed Baptist @doctorgill

And touching the house of the king of Judah, say,.... Or "to the house of the king of Judah" (p); that is, his palace, as Calvin understands it; go to it, and there say as follows, as in Jer 22:1; and some think that this part of the chapter belongs to that, and was not delivered at the time the former part of it was...