The only way to detect what is false in this world is to compare it to the truth and it is for this reason that we must be people of the Word. Peter's harshest criticism is leveled against the false teachers who must have been plaguing the Church by the time of this letter. Wherever you find truth you will find those that mimic it but the danger here is that it will not just affect your pocket book; it will decide your eternity. It is the reason why those who have been called to teach and preach must make sure they are not preaching their opinions but instead are standing square upon the Word of God. Too easy it is to allow our opinions on a matter to sway us without us realizing that this opinion is without substance. The fact is that anyone can "make" the Word of God say anything they want it to say but Peter warns of the destruction of such teachers:
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. (2 Peter 2:1-3)
Peter's description of the false teacher is not a flattering one and was so strong because these men were like bottom feeders, trying to use and abuse the weakest and young:
This is especially true of those who follow the corrupt desire of the sinful nature and despise authority. Bold and arrogant, these men are not afraid to slander celestial beings ... But these men blaspheme in matters they do not understand. They are like brute beasts, creatures of instinct, born only to be caught and destroyed, and like beasts they too will perish ... Their idea of pleasure is to carouse in broad daylight. They are blots and blemishes, reveling in their pleasures while they feast with you. With eyes full of adultery, they never stop sinning; they seduce the unstable; they are experts in greed—an accursed brood! They have left the straight way and wandered off to follow the way of Balaam son of Beor, who loved the wages of wickedness ... These men are springs without water and mists driven by a storm. Blackest darkness is reserved for them. For they mouth empty, boastful words and, by appealing to the lustful desires of sinful human nature, they entice people who are just escaping from those who live in error. They promise them freedom, while they themselves are slaves of depravity—for a man is a slave to whatever has mastered him. (2 Peter 2:10, 12, 13-15, 17-19)
Peter does not make any allowances here and neither should he. A person who leads others astray spiritually is leading them to their ultimate destruction. This is no game we are playing at here. We cannot pick and choose what we will listen to and what we will reject and what we will add to the Word of God. Those who are called to teach must leave self aside and teach only what they have been given to teach. It is an incredible responsibility and should never be entered into lightly because it carries with it a stronger punishment for straying from the path. Teachers must constantly check themselves and be sure that the only one who has mastery over them is the Lord Jesus Christ.
Another thing to note here is that followers of these false teachers are not given a break either. Certainly you may be seduced into the wrong path but you had a choice to listen or walk away. In the same way Eve was held accountable for her choice and Adam for his, even though they were seduced, we will be held accountable for not turning our back on the seduction. Teachers are nothing more than guides, trainers, helpers. They are not mediators between us and God. There are no mediators, physically or spiritually. We have direct access to the throne and the Holy Spirit is Jesus in us. We have the Word that we can check for ourselves and the Spirit to warn us. It is only when we allow someone to speak directly to our sinful/selfish nature, as Eve did, that we fool ourselves into believing the false to be the truth.
We live in an age when we are rich with information, but it is not all good information. Today in schools we train students to always consider the source, the reason why this source is involved in this information, the biases involved and just how reliable it is. The same must be true for everyone when it comes to the teachings we submit ourselves too; check the source for yourself. We are responsible for ourselves, our decisions, our actions and we will not be permitted to blame anyone else for what we decide. Know Jesus, listen to the Spirit, and know the Word of God. It is by these that you will be saved and will remain saved. Anything else will be burned away.