The same person who wrote 1 John to encourage believers also found it necessary to write to other churches where the false teachers might go to spread their ideas and practices. The letter of 2 John addresses one such gathering, referring to the church as a lady and its members as her children. The author describes the members of his own community as the children of your sister. (This was apparently typical of early followers of Jesus; there is a similar greeting at the end of 1 Peter.) He identifies himself as a church leader by using the title elder.
Apparently some people from this church had just come to visit him and he was pleased to learn that they were walking in the truth. He warns the church not to support the false teachers in any way. Despite its brevity, this letter expresses all of the themes that receive deeper development in 1 John.