Jeremiah 23:16
Thus saith the LORD of hosts, Hearken not unto the words of the prophets that prophesy unto you: they make you vain: they speak a vision of their own heart, and not out of the mouth of the LORD. Thus saith the LORD of hosts, Hearken not unto the words of the prophets that prophesy unto you: they make you vain: they speak a vision of their own heart, and not out of the mouth of the LORD.
The command is not to listen to the words of prophets who prophesy a vision out of their own heart rather than out of the mouth of the Lord. That human source includes a man's own ideas, imagination, and deceived imagination presented as a message from God. Such speaking does not convey God's word but makes those who hear it vain, filling them with vanity and false confidence. It misleads them and turns them away from the truth.
The characteristic false message is to assure those who despise God, reject Him, and walk after their own desires and imaginations that they shall have peace and no evil or harm shall come upon them. By contrast, true messengers speak God's word faithfully and turn people from their evil way and from the evil of their doings, while the false messengers who run without being sent face judgment. Unfaithful ministers fulfill this pattern by prophesying smooth, reassuring things that lead people to set aside God's law and to turn against those who keep it, until at last they themselves confess that they have deceived their hearers.
The same warning applies to claims to the prophetic gift when they foster fanaticism or are taken up for selfish ends. A claim to prophecy is not to be accepted merely because it is presented as a spiritual message. Messages offered as from God may instead come from a deceived human mind, and those who bring them have not been sent by God. False claimants may mix truth with error and use visions and sharp rebukes followed by flattery, so that their words are received as God's message.