What the Bible Has to Say About Heresy
So be on your guard! Remember that for three years I never
stopped warning each of you night and day with tears.
The Bible is the inspired and authoritative Word of God. It is written without error. But that doesn't mean that everyone agrees on the meaning of each verse. On the contrary, people have given Scripture many different meanings. Some use the Word of God to justify teachings that change the essential doctrines about the nature of God, the deity of Christ, the work of the Holy Spirit, or the nature of salvation by grace through faith in Jesus Christ (and possibly a few other primary doctrines). When you take a look at history, which we will do in future posts, and at the creeds of the Catholic Church (meaning universal, not Roman Catholic) before groups began to split off from one another (denominations), we learn what was universally agreed upon as the meaning of Scripture. This is very important in understanding why we believe what we believe rather than every person coming to their own conclusions about what Scripture means. Denominations came about when groups differed on non-essential doctrines.
When a person or its followers deviated from the essential doctrines, the Church would brand them as heretics or false teachers. The Bible warns us about those who teach another gospel. One of the ways we know a teacher is false is they teach something different than what Scripture traditionally meant. The apostles in the New Testament were given the authority to reveal and teach doctrine for the Church. But first, we will look at the Old Testament to see what it says about false prophets.
FALSE PROPHETS IN THE OLD TESTAMENT
The Old Testament talks about "prophets who prophesied lies (Jer 6:13; 27:14; Zech 13:3), deceived people with their dreams (Jer 29:8), prophesied by the authority of Baal (Jer 2:8; 23:13), threatened the lives of true prophets (Jer 26:7), and dared to speak when they had not stood in the council of Yahweh and received a word directly from the Lord (Jer 23:18). Typically, their prophecies promised peace when there was no peace to be had (Jer 6:14; 8:11; 14:3; 23:17; 28:2 & 11; Ezek 13:10; Micah 3:5)." 
One example is Elijah telling Ahab that he is the one who has caused trouble for Israel by abandoning the Lord's commands and following the Baals. Elijah tells Ahab to summon the people to meet him on Mount Carmel and "bring the four hundred and fifty prophets of Baal and the four hundred prophets of Asherah, who eat at Jezebel's table." (1 Kings 18:18-19). Another example is found in Jeremiah 23:9-40. Jeremiah addresses the many prophets who were speaking lies and leading the people of Israel astray and filling them with false hopes. He says these prophets speak visions from their own minds, not from the mouth of the Lord. How did Israel find themselves in this position? If we look back at Judges 3, we read that the Lord used the heathen nations that had not been driven out or the promised land, to test the Israelites to see whether they would obey the Lord's commands. Israel lived among these pagan nations and did what was evil in the sight of the Lord. They forgot the Lord their God and served the Baals and the Asherahs.
Prophets in the Old Testament were held to a very high standard. Deuteronomy 18:22 says, "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. do not be afraid of him." But even if what he prophesies does take place, "but he says, 'let us follow other gods' (gods you have not known) 'and let us worship them,' you must not listen to the words of that prophet or dreamer. The Lord your God is testing you to find out if you love him with all your heart and with all your soul. It is the Lord your God you must follow, and him you must revere...that prophet or dreamer must be put to death..." (Duet 13:2-5).
FALSE TEACHERS, PROPHETS, AND APOSTLES IN THE NEW TESTAMENT
What does the New Testament have to say about false teachers? "It is very difficult to draw a clear picture of the false teachers, but there are clues. Their teaching had ascetic elements (see 1 Tim 4:3; Titus 1:15) and a Jewish focus (see 1 Tim 1:7; Titus 1:10, 14; 3:9). It claimed special knowledge (1 Tim 6:20; Titus 1:16), asserted that the resurrection of the believers had already taken place (2 Tim 2:18, disrupted relationships (2 Tim 3:6-7; Titus 1:11), and might have emphasized salvation by works (2 Tim 1:9; Titus 3:5). Paul's strong response suggests a need to make corrections regarding the doctrine of Christ (see 1 Tim 2:5-6; 3:16; 2 Tim 2:8) and the last days (see 1 Tim 4:1-5; 2 Tim 2:18; 3:1-9; Titus 2:11-14). The false teachers opposed Paul's message, promoted immorality, and undercut the church's mission. Thus good leaders were needed (see Titus 1:10-13; 2:6-8, 15)." 
The New Testament has quite a bit to say about false prophets. "First of all, we should expect false prophets today, just as Israelites were to expect them in the past. Jesus warned of false prophets (Matthew 7:15-23; 24:23-25), as did the apostle Paul (Acts 20:28-31), and Peter (2 Peter 2:1), and John (1 John 4:1). They will not only come from without (2 John 1:4-11) but also from within (Acts 20:28-31; 2 Peter 2:12-22). Some of them may very well come with false wonders (Matthew 24:24; 2 Thessalonians 2:9). We must be constantly on the alert for such men and women, who will seek to lead us astray. As a rule, we can expect these folks to add to or take away from the Scriptures (see Deuteronomy 12:32; Revelation 22:18-19), or they will seek to twist the Scriptures (2 Peter 3:14-18). False prophets tell us what we want to hear, and they appeal to our fallen nature. They appeal to the flesh and our appetites, promising what they cannot deliver." 
Paul warns of false apostles as well. "In 2 Corinthians 11, the apostle Paul addresses the problem of false apostles invading the Corinthian church. He describes the false apostles as 'those who want an opportunity to be considered equal with us in the things they boast about' (verse 12). The book of 2 Corinthians is one of Paul's 'sarcastic' letters, as he contends with the church to recognize the error that had crept into their midst. He contrasts his selfless service with that of the 'super-apostles' (verse 5) who were seducing the church with their smooth speech and apparent wisdom. These impostors were pretending to be true servants of Christ, but they did not know the Lord. They were deceivers, preying on gullible Christians in Corinth to profit themselves and boost their ego. Paul chides the church that they 'even put up with anyone who enslaves you or exploits you or takes advantage of you or puts on airs or slaps you in the face' (verse 20). He even compares these impostors to Satan himself, who also 'masquerades as an angel of light' (verse 14)." 
The Bible has a lot to say about heresy even though it never uses the word. The word "heresy" comes from the Greek and means "choose." We typically use the word to describe "an opinion or belief that is the opposite of or against what is the official or popular opinion." In the Christian faith, we define the word as a" belief or opinion contrary to orthodox religious doctrine."  When someone or a group decides to choose a different doctrine over the orthodox one, we call them a heretic. Paul spent three years warning the Ephesians of false teachers, and it's interesting to note that in Revelation 2:2, Jesus commends the Ephesians for not tolerating evil people and for examining the claims of those who say they are apostles but are not. Paul also did not hesitate to call out false teachers, prophets, or apostles. Next post we will look at how believers are to respond to heresy.
 NLT Study Bible: Introduction to Paul's Letters to Timothy and Titus, p.2047; The Holy Bible, New Living Translation. Copyright 1996, 2004, 2015 by Tyndale House Foundation. Used by permission.