The Greek word (haiʹre·sis, from which comes the English word “heresy”) thus translated means “choice” (Le 22:18, LXX) or “that which is chosen,” hence “a body of men separating themselves from others and following their own tenets [a sect or party].” (Thayer’s Greek-English Lexicon of the New Testament, 1889, p. 16) This term is applied to the adherents of the two prominent branches of Judaism, the Pharisees and Sadducees. (Ac 5:17; 15:5; 26:5) Non-Christians also called Christianity a “sect” or “the sect of the Nazarenes,” possibly viewing it as a break-off from Judaism.—Ac 24:5, 14; 28:22.
The founder of Christianity, Jesus Christ, prayed that unity might prevail among his followers (Joh 17:21), and the apostles were vitally interested in preserving the oneness of the Christian congregation. (1Co 1:10; Jude 17-19) Disunity in belief could give rise to fierce disputing, dissension, and even enmity. (Compare Ac 23:7-10.) So sects were to be avoided, being among the works of the flesh. (Ga 5:19-21) Christians were warned against becoming promoters of sects or being led astray by false teachers. (Ac 20:28; 2Ti 2:17, 18; 2Pe 2:1) In his letter to Titus, the apostle Paul directed that, after being admonished twice, a man who continued promoting a sect be rejected, evidently meaning that he be expelled from the congregation. (Tit 3:10) Those who refused to become involved in creating divisions within the congregation or in supporting a particular faction would distinguish themselves by their faithful course and give evidence of having God’s approval. This is apparently what Paul meant when telling the Corinthians: “There must also be sects among you, that the persons approved may also become manifest among you.”—1Co 11:19.