2nd & 3rd John were written to particular individuals regarding their behavior in dealing with churches & the travelling teachers, for many deceivers have gone out. Christians were travelling around the Roman empire. John wrote this 60 yrs after the resurrection of Christ, as an elder in truth & love, a perfect balance like the love & mercy of God.

This reflects 2 types of churches we have these days, churches who accept anybody as long as they're "Christians" bringing in all kinds of doctrines. The true simple Gospel is lost. Another group of churches that exists today, just a one man-hero. Everybody else is not good enough, every other church has a problem, except him.  

What is the lesson? Be Careful, don't welcome those who come to shame God's name & to destroy God's work. We have a God of balance, perfect holiness & perfect love. That's what we should be too. May God grant us this simple balance! When people don't read these letters they have churches like these. May we see our selves in the word of God. All Holy, all loving.