What if the person relaying the false message misheard what god said or heard it from another source but assumed it was god saying it? Or what if they misinterpreted a sign from god and relayed a false message?
in other words they thought they were speaking the true word of god but unintentionally lied?
I'm asking hypothetically, as I'm an agnostic.
Prophecy is the gift of the spiritual child, so your query is largely obtuse in overlooking the nature of the spiritual activity that's performed by a prophecy.
Prophecy is seeing the unfolded present as an aspect of the final judgement, a false prophet has no connection to the judgement of truth, and thus deceives those who believe in the false-authority that the "prophet" makes representations for,— is the world or some part of it being glorified for a temporal attachment to the mere appearance of glory, or is the eternal spirit being expressed in an independent economy of purpose unto the reconciliation that overcomes all, even overcoming any slavish adherence to the faith itself. [[Even as Jesus used himself to exemplify the neo-Pagan worldview, to leave behind and share the divinity of his spirit at the cost of his own personage, so that in the end, Jesus Christ is the spirit of the begotten Son, never a mere vessel of personage: in the moment of 'his' greatest vulnerability, he impugned the integrity of the very claim he was being punished for making, to momentarily later prove those words to be the worthless folly of a bad example, the illustration of this simple mockery, conveyed at the expense of mocking the spirit of man through the body of that man, imparts a perfect example of overcoming the whole world: and let us not forget, there is no vicarious redemption, the Christian Doctrine says we must all pick up our cross and die daily, Jesus dying for our sin's is the language of an adopted Christ Consciousness, the neo-pagan style of belief in vicarious redemption is profanity to the real composition and operation the Church.]]
Most pertinent prophets, were doing the greatest of God's work by their interface with political endeavors, the most famous prophet in the old testament was saddled with engineering a King, when this very notion was a direct insult to God, but made necessary by the demands of men, forcing the development of the Judge role to emerge as a Son of Man, which is finally inculcated back into the body politic in the form of the church upholding communion in the Son the Man (communion through the members in particular).