(Ephesians 4:1-6) I, therefore, the prisoner of the Lord, beseech you to walk worthy of the calling with which you were called,If believers are united in this way, they can grow mature so they will not be "tossed to and fro by every wind of doctrine." (Ephesians 4:14)
2 with all lowliness and gentleness, with longsuffering, bearing with one another in love,
3 endeavoring to keep the unity of the Spirit in the bond of peace.
4 There is one body and one Spirit, just as you were called in one hope of your calling;
5 one Lord, one faith, one baptism;
6 one God and Father of all, who is above all, and through all, and in you all.
Heresies are the teachings that cause people to be tossed about.
Some heresies are teachings that are in direct conflict with the central teachings of Christianity. They attack doctrines like the inspiration and authority of scripture, the person and work of Jesus Christ, the nature of God, the basis of salvation, and so on.
Other heresies are divisions and dissensions over things that are not in the Bible at all.
Paul warned Timothy to study hard so that he would avoid stupid arguments over inane things. "Remind them of these things, charging them before the Lord not to strive about words to no profit, to the ruin of the hearers. Be diligent to present yourself approved to God, a worker who does not need to be ashamed, rightly dividing the word of truth. But shun profane and idle babblings, for they will increase to more ungodliness." (2Timothy 2:14-16)
In case he didn't get the point, Paul restates it. "But avoid foolish and ignorant disputes, knowing that they generate strife. And a servant of the Lord must not quarrel but be gentle to all, able to teach, patient," (2Timothy 2:23-24)
Still later Paul charges Timothy to preach the inspired, profitable Word of God. "For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; and they will turn their ears away from the truth, and be turned aside to fables. (2Timothy 4:3-4)
When he wrote to Titus he said the same basic thing. "But avoid foolish disputes, genealogies, contentions, and strivings about the law; for they are unprofitable and useless. Reject a divisive man after the first and second admonition, knowing that such a person is warped and sinning, being self-condemned." (Titus 3:9-11) The word translated, "divisive" here is "heretic."
Such heresies include legalistic rules about clothing, foods, and music. There are biblical principles that need to be applied, but an individual's good faith decision about application does not have the same force as scripture. The rules for such decisions are found in Romans 14.
In recent years the heresy of King James Onlyism has been blowing at gale force. The KJV has a long and distinguished history, but the whole spectrum of arguments that the KJV is the ONLY true Bible in the English language are at best "foolish disputes." At their worst they are a terrible betrayal of orthodox theology about the inspiration and authority of the Bible.
Heresies like these distract people from the clear teachings of the Bible about things of eternal importance. We should avoid such things and expose them whenever possible.