New Defender's Study Bible Notes
3:10 heretick. This is the only occurrence of the Greek word hairetikos in the New Testament (though its derivative, “heretic” has been used frequently in church history). The similar word, hairesis (translated “heresy” or “sect”) occurs nine times. It was applied by the Jews to the Christians, and by the Christians to the Pharisees and Sadducees (Acts 5:17; 15:5; 24:5). Both Greek words are derived from hairetizo, meaning “choose.” There is no inherently evil meaning suggested, but simply a marked difference from a standard teaching. A heresy only becomes wrong when it substantially contradicts a clear doctrine of Scripture (e.g., theistic evolution, denial of the virgin birth).
3:10 reject. The Greek word here means “avoid” or “refuse,” but not necessarily “excommunicate.” If a heretic refuses a second admonition, however, his ideas should at least be ignored by the church. That this has not been done is evident in the widespread departure of churches and entire denominations from the true Christian faith. Even modern evangelical churches are being seriously undermined today by theistic evolutionism, humanistic psychology and other heresies that have been allowed to thrive therein, having first been promoted in their associated religious colleges and seminaries.