The apostle John is an old man now overseeing a network of house churches around the city of Ephesus. It seems these communities were made-up mostly of believers from a Jewish background, and they had recently gone through a crisis that motivated John to write these epistles.
He mentions a group of estranged people who now deny Jesus as Messiah and the son of God. (See 1 John 2 and 4) They are stirring up hostility among those who stayed faithful to Christ and his church.
2nd and 3rd John clearly addressed this conflict. 2nd John is a warning to a specific house church not to validate or support these deceivers who deny Jesus. This church community is not to offer any.
3rd John is written to Gaius, a member of one of these house churches, and he is asked to welcome legitimate missionaries who will to arrive soon.
These letters give us a window into the tension and conflict that John faced in these churches.