The theme of II John is that of false teachers. The nineteenth of the Epistles was written from Ephesus sometime around 93 AD by the apostle John; the last surviving of the 12 disciples of Jesus. They are still causing problems for the church, wandering around trying to convert people to follow them. John fears that these itinerant preachers might take advantage of the good hearted Christians, and so he warns them not to listen to those who do not speak the truth about Jesus.
II John 1:5-6
"And now I beseech thee, lady, not as though I wrote a new commandment unto thee, but that which we had from the beginning, that we love one another. And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it"