Thomas Aquinas Commentary Jeremiah 29:23

"because they have wrought folly in Israel, and have committed adultery with their neighbors` wives, and have spoken words in my name falsely, which I commanded them not; and I am he that knoweth, and am witness, saith Jehovah." — Jeremiah 29:23 (ASV)

v.23a

Here, he speaks of their guilt:

1. Adultery: folly, that is, a foolish thing; and adultery. Thus you would do to the daughters of Israel, and they for fear would speak with you (Daniel 13:57). As it says above: each one neighing at the wife of his neighbor (Jeremiah 5:8).
2. The lie: and they spoke a word in my name falsely, for they were saying that liberation was near and that the Christ was to be born from them, so that they might in this way deceive the women into committing adultery. As it says above: I did not speak to them, yet they prophesied (Jeremiah 23:21).

v.23b

Here, he speaks of the justice of the judgment: judge, to inflict punishment; witness, to convict of guilt—because by divine assent, they were miraculously discovered. The Lord stirred up the spirit of a young boy, whose name was Daniel (Daniel 13:45).