1 Timothy 6:2-3 BSB “3 If anyone teaches another doctrine and disagrees with the sound words of our Lord Jesus Christ and with godly teaching, 4 he is conceited and understands nothing. Instead, he has an unhealthy interest in controversies and semantics, out of which come envy, strife, abusive talk, evil suspicions”
The test of a genuine Christian is in what they believe, teach, and preach. If they adhere to another doctrine, alienated from that which Christ preached, and reject the core and fundamental message of the gospel with the rest of the New Testament, it reveals their spiritual condition. Tread lightly from such people, or they may entrap your soul with deceptive words.
5 We did not give in to them for a moment, so that the truth of the gospel would remain with you. -Galatians 2:5 BSB
Paul told the saints in Galatia that if he and his companions did not resist them and fought for the truth of the gospel, they (the church in Galatia) would have never received and continued with the true gospel of Jesus Christ.
This verse shows us that we can never give in to false doctrine or allow false believers to spread their unbiblical message to others if we can help it. Especially if you become aware that their deceptive message is reaching those you are trying to influence to follow Christ and walk in the truth. If you don’t battle false teachers, they will undo everything you had begun to do for the Lord Jesus Christ.