Jeremiah 21:12 - Matthew Poole's English Annotations on the Holy Bible

He calls these the house of David, either checking them, who were indeed so in a lineal descent, or minding them what they ought to be in imitation of their father, David. The only way they had to keep off those Divine judgments which now hanged over their heads was to execute judgment, that is, justice, without partiality; the prophet's advice to them to execute judgment in the morning either lets them know they must do it quickly, or else it hath respect to the time when the courts of justice sat. One species of justice was the deliverance of the oppressed from the hands, that is, from the power and malice, of the oppressors; which if it were not done, God threateneth certain ruin and destruction to them, which none should be able to hinder or avoid. The cause of which was, their wicked doings; for that God who doth people good, and showeth them favour, not for their sake, but for his own name's sake, yet never punisheth them but for a cause found in them.