John Gill Commentary Jeremiah 23:16

"Thus saith Jehovah of hosts, Hearken not unto the words of the prophets that prophesy unto you: they teach you vanity; they speak a vision of their own heart, and not out of the mouth of Jehovah." — Jeremiah 23:16 (ASV)

Thus says the Lord of hosts, do not listen to the words of
the prophets that prophesy to you
Do not hear them; stop your ears at what they say; give no credit to them. The Targum is, ``do not receive the words of the false prophets that prophesy to you:''

they make you vain ;
they filled their heads with vain and empty things, and their hearts with vain hopes, which deceived them; so the Targum, ``they deceive you;'' they taught them vain things, and made them vain and sinful in their lives and conversations; and therefore were not to be listened to:

they speak a vision of their own heart, [and] not out of the mouth of
the Lord ;
what they imagined they saw was a device of their own hearts, and what was agreeable to them, which must be bad enough; a produce of their own brains; an invention of their own; mere doctrines of men, and not such as come from the mouth of God, are his revealed will, and according to his word; and therefore not to be listened to; for nothing is to be heard and received, in matters of religion, but what is according to the revelation of God's will in his word; see (Isaiah 8:20) . The Targum is, ``they speak to you the wickedness of their hearts, and not by the word of the Lord.''