How can I tell a heresy or cult?

What the Bible says

Discerning a heresy means walking between two dangers. One is believing anything at all; the other is suspecting everyone who differs from us. Scripture warns against both. On the first, John writes:

Beloved, do not believe every spirit, but test the spirits to see whether they are from God. For many false prophets have gone out into the world.

1 John 4:1

The test follows at once: "Every spirit that confesses that Jesus Christ has come in the flesh is from God" (1 John 4:2). The first mark, then, is Christ. Who is Jesus? Did God truly become man? Are his cross and resurrection the centre of salvation? See Is Jesus God?.

The second mark is the gospel. When the Galatians began to follow something other than what Paul had taught them, he spoke with unusual force.

As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be under a curse!

Gal 1:9

The issue was adding something to salvation by grace. A teaching that adds conditions beyond Christ, and a teaching that turns grace into permission to do as one pleases, are both "another gospel." Paul adds that it "is not even a gospel" (Gal 1:7). The gospel is not ours to improve; it is received.

The third mark is fruit. Jesus warns:

Beware of false prophets. They come to you in sheep’s clothing, but inwardly they are ravenous wolves.

Matt 7:15

Appearances alone will not expose them, so Jesus says, "By their fruit you will recognize them" (Matt 7:20). Fruit is the life a teaching produces. Peter names the fruit of false teachers: "In their greed, these false teachers will exploit you with deceptive words" (2 Pet 2:3). A teaching that drains people’s money and freedom deserves a hard look. Jesus also described how leaders should behave: "It shall not be this way among you. Instead, whoever wants to become great among you must be your servant" (Matt 20:26). A leader who dominates and will not be questioned is a poor sign.

From these tests come warning signs: a leader who claims to be the Christ or a special saviour, a new revelation or private interpretation set above Scripture, and secrecy and control. Jesus told us in advance, "if anyone says to you, ‘Look, here is the Christ!’ or ‘There He is!’ do not believe it" (Matt 24:23). On date-setting he said:

No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father.

Matt 24:36

Anyone who claims to know the date of his return contradicts what the Son himself said. And truth does not fear examination. The Bereans were praised because they "examined the Scriptures every day to see if these teachings were true" (Acts 17:11). A group that discourages questions, will not let you check the Bible for yourself, or separates you from family and other churches deserves great caution for that reason alone.

The church's witness

The church has long done this work. It confessed the most basic things in its creeds: Father, Son and Spirit; Christ truly God and truly man; the cross and the resurrection at the centre The Nicene Creed. On other matters, such as the mode of baptism, predestination and free will, the gifts of the Spirit, and the order of the last things, faithful churches differ while confessing the same creed. Those differences are not heresy (Why are there so many churches and denominations?). Paul tells the Romans not to despise a brother who sees things differently.

Matthew Henry, on 1 John 4:1, writes, "The sum of revealed religion is in the doctrine concerning Christ, his person and office" Matthew Henry. On Galatians 1 he gives the spirit in which to act: "In reproving others, we should be faithful, and yet endeavour to restore them in the spirit of meekness" Matthew Henry.

Augustine asks why Jesus follows the narrow gate with a warning about false prophets. His answer is that it was to keep out "heretics, who often commend themselves because of the smallness of their numbers" Augustine. Smallness proves nothing. Jerome warns of those who, "by observing temperance, chastity, and fasting, surround themselves as it were with a garment of sanctity," while their hearts are poisoned Jerome. On Matthew 24 he adds that if anyone says Christ is hidden away in some secret place, "believe Him not" Jerome.

In the original languages

The Greek pseudoprophētēs (ψευδοπροφήτης), "false prophet," joins "false" and "prophet" and describes someone who pretends to speak for God.

Hairesis (αἵρεσις), the word behind "heresy," originally meant a "choice" or a "party." In Acts it can simply name a school within Judaism, such as the Sadducees. In 2 Peter 2:1 it has become "destructive heresies" that deny the Master, and in Titus 3:10 the related hairetikos (αἱρετικός) is a person who stirs up division. The word thus carries both a doctrinal question and one about division.

The "test" of 1 John 4:1 is dokimazō (δοκιμάζω), the word for assaying metal to see whether it is pure. It is the same verb as in "Test all things" (1 Thess 5:21). Scripture does not say only "doubt"; it says test, and hold what is good.

Common objections

"Isn’t ‘heresy’ just the name the winners give the losers?" There is truth here. In church history the word has been used as a weapon by those in power and has led to cruelty. Even today it is sometimes thrown at churches whose theology differs only slightly. But misuse does not show that there is no standard. The warnings of John and Paul come before any later council, and standards such as Christ’s true humanity and the gospel of grace are in the New Testament itself. So before using the word, one should be able to say exactly where a teaching departs from them.

"They are kind and devoted people. If the fruit is good, why be suspicious?" This is not a weak objection. Chrysostom admits that "among heretics it is possible many times to find a good life" Chrysostom. Warmth and zeal do not guarantee that a teaching is true. Augustine says that even fasting, almsgiving and prayer can be a sheep’s clothing when done to be seen, yet he adds that "the sheep ought not to hate their own clothing because it is often used to hide wolves" Augustine. What matters is where zeal points; teaching about Christ and the life it produces must be weighed together.

"Doesn’t this just teach people to distrust anyone different?" The danger is real, which is why the core must be separated from the periphery. The core is Christ and the gospel; on the rest, Christians may differ. Scripture tells us to test, and to do it in "the spirit of meekness."

Going further

People usually ask this for one of two reasons: they worry about a group they are in, or someone they love has joined one. For the first, there are questions to ask. What does it teach about Jesus? Can I read the Bible and ask questions freely? Am I free to leave? Are my family relationships healthier or weaker? For the second, ridicule and argument push people further in. Keep the relationship, listen, ask questions rather than trying to win, and read the Gospels together if they are willing. Above all, keep a door open for them to come back. If needed, ask a trustworthy pastor or counsellor for help.

You might ask yourself: Can I tell which of my beliefs are core and which are opinions? Am I quick to condemn believers who see things differently? Are questions welcome where I worship?

To read further, see What is the gospel? and How should we read the Bible?