It is addressed to "the elect lady," and closes with the words, "The children of thy elect sister greet thee;" but some would read instead of "lady" the proper name Kyria. Of the thirteen verses composing this epistle seven are in the First Epistle. The person addressed is commended for her piety, and is warned against false teachers.
The language of this epistle is remarkly similar to 3 John, and it is the scholarly consensus that the same man wrote both of these letters, although it has been doubted he also wrote the Gospel of John, the First Epistle, or Revelation.
John wrote this letter "to the elect lady and her children." This is either a figurative reference to a church community or a literal reference to a specific person.
John may have used the title Elder as an affectionate description of himself, since his authority as an apostle would not be in question at this late date.
John affirms the deity of Jesus by affirming the Son's equality with the Father.
According to 2John 10, we are not to receive into our homes or even greet anyone who comes to us and does not believe that Christ is come in the flesh.
So, apparently, John is here warning against (1) allowing a false teacher into the church, and (2) giving this false teacher a platform from which to teach.
John is directing the church not to extend this kind of hospitality to teachers of false doctrine.