But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves. 2 Peter 2:1
False prophets of old and the false teachers of Peter’s day preyed on the people’s ignorance of scripture. Both brought heresy alongside truth (their own choices, opinions). Both purposely introduced what they wanted to see in the future, and in scripture, to acquire power or wealth, or likely both. Both said things to tickle the ears. And nothing has changed since then.
For the time will come when they will not endure sound doctrine; but wanting to have their ears tickled, they will accumulate for themselves teachers in accordance to their own desires. 2 Timothy 4:3
Know this. False prophets fail the test of time. Only authentic prophets of the Lord utter what will be proven true in the future. And it’s important to understand in this day, the office of prophet or gift of prophecy is the act of pronouncing canonized scripture, nothing more or less. For example, Peter was writing and transmitting “2 Peter.” He had nothing more to add after that, or else there would have been “3 Peter.”
As for teachers, only God’s truth withstands close scrutiny. Sound biblical teachers cut it straight. What is taught is “healthy.”
We are no longer to be children, tossed here and there by waves and carried about by every wind of doctrine, by the trickery of men, by craftiness in deceitful scheming. Ephesians 4:14
Be diligent to present yourself approved to God as a workman who does not need to be ashamed, accurately handling the word of truth. 2 Timothy 2:15
To spot heresy, you must first be a student of sound doctrine.
In pointing out these things to the brethren, you will be a good servant of Christ Jesus, constantly nourished on the words of the faith and of the sound doctrine which you have been following. 1 Timothy 4:6
Practically, be on the look out for the words, “I think,” and for opinions and interpretations contrary to the “verily, verily” statements of Jesus Christ (that is, “truly, truly”). For example, “Truly, truly, I say to you, he who believes has eternal life. John 6:47
If anyone advocates a different doctrine and does not agree with sound words, those of our Lord Jesus Christ, and with the doctrine conforming to godliness, he is conceited and understands nothing; but he has a morbid interest in controversial questions and disputes about words, out of which arise envy, strife, abusive language, evil suspicions, and constant friction between men of depraved mind and deprived of the truth, who suppose that godliness is a means of gain. 1 Timothy 6:3-5