Charles Ellicott Commentary Jeremiah 23:31

"Behold, I am against the prophets, saith Jehovah, that use their tongues, and say, He saith." — Jeremiah 23:31 (ASV)

That use their tongues, and say, He saith.— Literally, that take their tongues. There is no adequate evidence for the marginal rendering “that smooth their tongues.”

The scornful phrase indicates the absence of a true inspiration. These false prophets plan their schemes, and take their tongue as an instrument for carrying them into effect.

The formula which they used, “He saith,” was not the word for common speaking, but that which indicated that the speaker was delivering an oracle from God. (See Note on Jeremiah 23:17.) Elsewhere the word is only used of God, but the prophet, in his stern irony, uses it of the false prophets, they say oracularly. This is an oracle.