Have you ever been at a religious meeting, or a party, or a conference and the compere or host stepped up to the microphone and said something like, “Now we will hear a few words from a distinguished false prohpet”? Have you ever been given a business card or read a telephone directory entry where the person's occupation was given as “false prophet and professional liar”?
If you answered “yes” to either question then you are probably one of a small minority on the planet Earth. However, if the New Testament authors are to be believed we ought to be encountering false prophets and professional liars quite regularly. The New Testament authors (Matthew, Mark, Luke, John, Paul, Peter, James, Jude) all gave warnings about the deceivers that had, in their time, already emerged and about those that would come in the future. In fact, if the number of times that they mention such things is any measure of how important they thought it was, this is a pretty major topic and ought to be prominent in any Christian's meditation.
So where are they, these false teachers, these barren trees and angels of darkness clothed in light? Where are they all lurking?
“Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves. By their fruit you will recognise them. Do people pick grapes from thorn bushes, or figs from thistles? Likewise every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus, by their fruit you will recognise them.”
“Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?' Then I will tell them plainly, 'I never knew you. Away from me, you evildoers!”
As Jesus was sitting on the Mount of Olives, the disciples came to him privately. "Tell us," they said, "when will this happen, and what will be the sign of your coming and of the end of the age?" Jesus answered: "Watch out that no one deceives you. For many will come in my name, claiming, 'I am the Christ,*' and will deceive many. You will hear of wars and rumours of wars, but see to it that you are not alarmed. Such things must happen, but the end is still to come. Nation will rise against nation, and kingdom against kingdom. There will be famines and earthquakes in various places. All these are the beginning of birth pains.  "Then you will be handed over to be persecuted and put to death, and you will be hated by all nations because of me. At that time many will turn away from the faith and will betray and hate each other, and many false prophets will appear and deceive many people.
For false Christs and false prophets will appear and perform great signs and miracles to deceive even the elect -- if that were possible. See, I have told you ahead of time.
2nd Corinthians 11:13.
... For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. And no wonder, for Satan himself masquerades as an angel of light. It is not surprising, then, if his servants masquerade as servants of righteousness. Their end will be what their actions deserve.
2nd Peter 2:1.
But there were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies, even denying the sovereign Lord who bought them -- bringing swift destruction on themselves. Many will follow their shameful ways and will bring the way of truth into disrepute. In their greed these teachers will exploit you with stories they have made up. Their condemnation has long been hanging over them, and their destruction has not been sleeping.
1st John 4:1.
Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world.
But the beast was captured, and with him the false prophet who had performed the miraculous signs on his behalf. With these signs he had deluded those who had received the mark of the beast and worshiped his image. The two of them were thrown alive into the fiery lake of burning sulphur.
Matthew 12:39. He answered, “A wicked and adulterous generation asks for a miraculous sign! But none will be given it except the sign of the prophet Jonah.”
Matthew 16:4. A wicked and adulterous generation looks for a miraculous sign, but none will be given it except the sign of Jonah." Jesus then left them and went away.
Mark 8:38. If anyone is ashamed of me and my words in this adulterous and sinful generation, the Son of Man will be ashamed of him when he comes in his Father's glory with the holy angels."
James 4:4. You adulterous people, don't you know that friendship with the world is hatred toward God? Anyone who chooses to be a friend of the world becomes an enemy of God.