What does 2 John 1:9 mean?
Following his warning, John provides a way to identify false teachers. First, he notes that those who do not hold to sound teaching are worthy of doubt. In other words, if a person teaches something about Jesus Himself which is grossly wrong, they cannot be considered a believer. True Christians may misunderstand or be ignorant of certain biblical teachings about Jesus. But those who completely misunderstand who Jesus really was, or who teach against the true identity of Jesus on purpose, are false teachers and unbelievers.In contrast, those who stay faithful to Christ's teachings should be trusted. The idea of "abiding" is again mentioned (2 John 1:2). A true believer will last in the faith; he or she will not later deny Christ and teach falsely about Him. This verse may also help those who wonder about people who have appeared to be strong Christians and then later deny Christ or become aberrant in their faith. John says such people do not have the Son; in other words, they were never truly believers in Jesus.
Second John 1:7–11 discusses a certain type of false teacher. Those who deny that Jesus came to earth in a real, physical, human form are not teaching the truth. According to John, these people are not to be supported in any way whatsoever. Those who help a false teacher are participating in their sin.
The entire book of 2 John is only 13 verses long. It is written by ''the elder,'' in this case the disciple John. In it, John commends a group of believers for holding fast to the truth of the gospel. He also warns these people to avoid those who deny aspects of the Christian faith, and who deceive people away from the truth. John uses the term ''elect lady and her children'' as a reference to this entire local church.