2 John is a single chapter and it is pretty short. Essentially it is the ancient equivalent of snopes.com or factcheck.com. It is warning the members of a church (who the author – probably the disciple John – calls the lady chosen by God and her children) about false teachers that are travelling around spreading a false gospel.
It essentially says that if the teacher does not teach about Jesus Christ coming in the flesh then they are wrong. He also reminds the church to continue in love.
This short letter is actually quite a helpful lesson in the age of fake news. What are the main criteria of what we consume, post and share? Well, perhaps that it promotes love and testifies of Jesus Christ? I wonder what social media would look like if we followed those rules.