Some think the Hebrew words were more properly translated smooth their tongues: see the English Annotations. But the next words seem to assure us that the crime for which God here by the prophet reflecteth upon the false prophets, was not so much their flattering people, and speaking to them such smooth things as pleased them, as their entitling of God to their lies, saying, He, that is, the Lord, saith. So it may be, though the word might be translated smooth, yet it is her, better translated use.
Related Commentaries of Jeremiah 23:31
Jeremiah 23:31
31 Behold, I am against the prophets, saith the LORD, that use their tongues, and say, He saith.