1. Knows that what they say and do is false, but enjoys deceiving others (a liar)
2. Believes what they say is true even when faced with contrary evidence (a deluded person)
3. Believes the ends justifies the means (a pragmatist with a twisted morality)
4. Needs the approval of others to function (a broken person)
5. Has two agendas: appear upright to others but cultivates a sinful life (a hypocrite)
It is hard to tell which kind of person you are confronting here. The common denominator is a level of deception, either to oneself, to others or both. But if we understand the person's true motive, does it really matter? Deception is deadly to one's faith, walk in Christ and maybe even their salvation. Deception was at the core of Satan tempting Eve: "Did God really say?" (Gen. 3:1) This was not a mere inquiry to the nature of God's instructions to Adam and Eve. It was a loaded question, designed to lead Eve down a path of questioning the truth of God and then to deceive her about the truth of God.
Satan's tactics have not changed: deception and death are always the endgame.
But sometimes we are mystified about what is driving the person to teach and behave the way they do. Our feelings are not always a good indicator, for even if our feelings are positive, we are still stepping into the lion's den. Or maybe our intuition says, "Red flag!" but we talk ourselves out of it, for we feel guilty seeing this person in less of a positive light. Or we know the Scripture so well, we can clearly identify when the teachings are wrong, but we like the person, and so we don't know how to approach them to correct their error. It's easy to castigate a false teacher on TV, but when you are faced with someone who actually believes that person on TV, it's another matter.
Again, let's go to the Word, and see what it says about false teachers.
Jeremiah 23:16: "This is what the Lord Almighty says: 'Do not listen to what the prophets are prophesying to you; they fill you with false hopes. They speak visions from their own minds, not from the mouth of the Lord.'"
"False hopes" is a perilous form of deception, for when those hopes are too delayed in coming, or don't appear as if they ever will come, then a person's faith is rocked, maybe even shattered. But that is Satan's goal. He doesn't want you to simply be disappointed. He wants you to ultimately reject God.
Prophets spoke in God's name; so if what they said didn't come to pass, it would be very simple to equate God's word with a lie. But Jeremiah is saying that just because someone claims to be a prophet, does not make them one, even if what they say seems right. (If the words were so obviously wrong, no one would regard the prophet as such, and would cease to listen. There will be just enough truth to give credence to the prophet's claim, but enough lies to deceive the listeners.)
Deuteronomy 18:18-22 sets the standard: "I will raise up for them a prophet like you from among their fellow Israelites, and I will put my words in his mouth. He will tell them everything I command him. I myself will call to account anyone who does not listen to my words that the prophet speaks in my name. But a prophet who presumes to speak in my name anything I have not commanded, or a prophet who speaks in the name of other gods, is to be put to death.” You may say to yourselves, “How can we know when a message has not been spoken by the Lord?” If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously, so do not be alarmed."
There. If the prophet is deluded about on whose behalf he speaks or is manipulating others, it matters not: He is deceiving the people as to what God would have them know. If a "word from the Lord" leads to a wrong action, wrong belief, or to the start of a person falling away, God is just in His wrath against such a person who perpetrated the lie.
Prophesy is still a part of the picture in the New Testament: "Now to each one the manifestation of the Spirit is given for the common good. To one there is given through the Spirit a message of wisdom, to another a message of knowledge by means of the same Spirit, to another faith by the same Spirit, to another gifts of healing by that one Spirit, to another miraculous powers, to another prophecy, to another distinguishing between spirits, to another speaking in different kinds of tongues, and to still another the interpretation of tongues. All these are the work of one and the same Spirit, and he distributes them to each one, just as he determines." (1 Cor. 12: 7-11) [emphasis mine]
Look at the word "prophecy" and its meanings as outlined by Strong's:
And when the New Testament writers spoke of the prophets in the Old, here is what they meant: "of the prediction of events relating to Christ's kingdom and its speedy triumph, together with the consolations and admonitions pertaining to it, the spirit of prophecy, the divine mind, to which the prophetic faculty is due"
So, if the OT prophets were ultimately speaking of Christ, then there can be no lies tainting their words. Hence, the utter strictness of God's standard in Deuteronomy 18.
If the NT writers saw the OT prophets as speaking of Christ, they accepted their utterances as truth, for only truth can point to the ultimate truth: Christ Himself. He even said that He was Truth itself.
That is why deception is so dangerous, for it leads us away from the truth and from The Truth.
Satan steals us away by leading us away and he doesn't care who he uses. His goal? To destroy and kill us. (John 10:10)