John was writing to a Christian lady who had a reputation for godly hospitality.  She was kind and generous and thought the best of strangers.  But John was concerned that she might naively welcome travelling teachers who were perverting the gospel and teaching error about the Lord Jesus Christ.  So John urged her to guard her home, and the church which probably met there, from false teaching (2 Peter 3:17).

False teaching always centres upon the person of the Lord Jesus Christ, and what He taught.  So to say that He is not the Son of God, God in a human body, God with us; or that He did not die or that He had no bodily resurrection or that He did not ascend to heaven or that He will not return or that His teachings are mistaken … all that is false teaching.  The apostles were appointed as His official interpreters by the help of the Holy Spirit (Acts 1:8).  To reject their written instructions and replace it by something more convenient is also false teaching.

Discernment starts with the revelation of God's truth to the apostles as recorded in the New Testament.  The Holy Spirit affirms these truths to our consciences (John 16:12-15).  Every time we open our home or church to strangers who claim to have a message from God, we need to be sure that they believe what the apostles wrote.  Some may say that if Jesus accepted invitations to meet with morally bad people, then we should simply accept everybody.  But the point is that they invited Him, and He gave the teaching: Jesus did not recommend that the apostles should welcome false teachers – quite the opposite (Matthew 7:15; Matthew 24:23-25).

Guard your heart, guard your home, guard your church (1 Timothy 6:20-21).  Do not let false teaching corrupt you or those you love.  Be careful who you welcome to teach you and those who are dear to you.  To give airtime to error is to be an active participant in the corruption of the gospel and the dishonouring of Jesus Christ.  Do not assume that everybody who comes to your door or visits your church wants to submit to Christ; some want to draw people away from Him (Acts 20:29-31).  Yes, we should love everybody, but no, we should not give them space to exert a wrong authority and wreck the faith of vulnerable people.