Thomas Aquinas Commentary Jeremiah 21:1-6

"The word which came unto Jeremiah from Jehovah, when king Zedekiah sent unto him Pashhur the son of Malchijah, and Zephaniah the son of Maaseiah, the priest, saying, Inquire, I pray thee, of Jehovah for us; for Nebuchadrezzar king of Babylon maketh war against us: peradventure Jehovah will deal with us according to all his wondrous works, that he may go up from us. Then said Jeremiah unto them, Thus shall ye say to Zedekiah: Thus saith Jehovah, the God of Israel, Behold, I will turn back the weapons of war that are in your hands, wherewith ye fight against the king of Babylon, and against the Chaldeans that besiege you, without the walls; and I will gather them into the midst of this city. And I myself will fight against you with an outstretched hand and with a strong arm, even in anger, and in wrath, and in great indignation. And I will smite the inhabitants of this city, both man and beast: they shall die of a great pestilence." — Jeremiah 21:1-6 (ASV)

Here the threat is given against the kings, who hold the highest rank in secular power. They will be punished in two ways:

1. First, in that the kings will be punished through the punishment of the people.
2. Second, in that they will be punished in their own person, as it says, thus says the Lord (Jeremiah 22:1).

Concerning the first point, two things are presented.

1. First is the king's question or petition: inquire—as if to say, “Seek a divine response”—and pray for us. This Pashhur is not the same as the one mentioned previously, who was born of a different father (Jeremiah 20:1). As Isaiah says, This day is a day of tribulation, and correction, and blasphemy; for the children have come to birth, and there is no strength to bring them forth (Isaiah 37:3). And further on in the same passage: raise a prayer for the remnant which is left (Isaiah 37:4).
2. Second is the prophet's response: and Jeremiah said. In this response, he first threatens punishment regarding the time before the city’s capture, targeting the three things in which they trusted.

First, they trusted in the protection of their weapons, against which the prophet says, behold I will turn. This is as if to say, “The weapons you have taken up against the enemy will be turned against you, because you will fight one another.” As the Psalm says, His sorrow shall be turned on his own head, and his iniquity shall come down on his own crown (Psalms 7:17). Alternatively, the phrase they will be turned back means they will act without effect.

Second, they trusted in the strength of their walls, against which he says, and the Chaldeans, who besiege you round about the walls. This is as if to say, “The walls will not prevent them from entering.” As Lamentations says, The kings of the earth and all the inhabitants of the world did not believe that the adversary and the enemy would enter through the gates of Jerusalem (Lamentations 4:12).

Third, they trusted in divine protection, against which he says, I shall defeat you with an outstretched hand—that is, with My power prepared for vengeance. He continues: with a mighty arm, which cannot be resisted; with fury, regarding the wicked; and indignation, regarding those who sin less; and great wrath, against those who sinned moderately.