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Sometimes the term heresy gets thrown around too freely. Not every disagreement about Scripture is heresy. But there is no doubt that genuine heresy is a serious matter. Less than a generation after the Church’s birth at Pentecost, false teachers were already twisting the truth about Jesus. Heresy was a dangerous threat to the Early Church, and it’s still a dangerous threat today. But what exactly is heresy?

Basically, heresy is a denial or distortion of Christian teachings. That might not sound too serious, but 2 Peter 2:1 says that heresies lead to destruction—both for those who teach them and for those who believe them. Heresies have caused division in the Church for the last two thousand years. And the heresies being taught today are surprisingly familiar. They are usually just ancient heresies that have been updated for a modern audience. With that in mind, let’s quickly look at five heresies the Early Church had to fight against. Not only will this help us understand Paul’s concerns about false teachers, but it will help us stand against heresy in our own day and time.

Gnosticism gets its name from the Greek word for “knowledge.” Gnostics believed that salvation could be achieved by knowing secret, spiritual mysteries. They also believed in dualism, which is an incorrect belief that the material world—including the human body—is evil and only spiritual things are good.

Marcionism was named after its founder, Marcion, a ship owner who lived in the second century. Marcion spread the false teaching that there were two gods: One was the creator god of the Old Testament, who operated as a harsh judge. And the second was the good god of the New Testament, who sent Jesus to redeem humanity.

Sabellianism was named after its founder, Sabellius, and is also sometimes called modalism. Sabellianism denies the Trinity and instead teaches that God has revealed His nature in different modes throughout history—first as the Father, then as the Son, and now as the Holy Spirit.

Docetism gets its name from the Greek word meaning “seem.” For the Docetists, what “seemed” to be unbelievable was the physical body of Christ. The teachings connected to Docetism all deny that Jesus came in a material, bodily form.

Arianism was named after its founder, Arius, who spread the false teaching that Jesus was a created being instead of existing eternally with the Father. Part of this heresy came from Arius’ belief that God the Father was unknowable and that Jesus could be known by humans only if He had been created.

So how do we fight against heresies like these? First, study God’s Word. Knowing His truth will help you recognize what’s fake. Second, rely on godly, trustworthy sources. Pastors, teachers, and official doctrinal statements can help keep you on course. Finally, focus on what Scripture focuses on. Hebrews 13:9 cautions us not to get carried away by “strange doctrines.” Instead, we should hold tightly to the core teachings that have been faithfully passed on to us.