John Gill's Exposition of the Whole Bible
Jeremiah 29:23
Because they have committed villany in Israel,.... Or "folly" f; as the sins of adultery, and prophesying falsely, are afterwards mentioned. This was not the reason why the king of Babylon put them to death; though the Jews g have a tradition that they attempted the chastity of Nebuchadnezzar's daughter, for which reason he case them into a furnace; but rather it was on account of their prophesying immediate destruction to Babylon; and telling the captives that they should be delivered in a short time; and stirring them up to prepare to go to their own land; but the reasons here given are those which moved the Lord to deliver them into the hands of the king of Babylon for their destruction:
and have committed adultery with their neighbours' wives; which was a piece of villany, as well as folly; and which abundantly showed that these men were not the prophets of the Lord, or were sent by him, being such impure wretches:
and have spoken lying words in my name, which I have not commanded them; as that the people should return to their own land in a short time; this was another part of their villany and folly, and for which they were given up into the hands of the king of Babylon, to be punished:
even I know, and [am] a witness, saith the Lord; for though their adulteries might be very secretly committed, and their lying prophecies were not seen to be such by the people in common; yet God, who is omniscient, saw all their impurity, and knew all their lies and falsehood, and was, and would be, a swift witness against them, here and hereafter. The Targum is,
"and before me it is manifest, and my word is a witness, saith the Lord.''
f נבלה "stultitiam", V. L. Schmidt. g T. Bab. Sanhedrin. fol. 93. 1.