These two brief letters are written by the apostle John in his old age, probably in his nineties. These two short little letters are an encouragement to abide in the sound doctrine of Christ and to watch out for evil that creeps into the church.
Second John is written to a Christian lady. Many have tried to figure out what or who this lady “symbolized.” The standard interpretation is that it is the church, but I see no reason to not take “lady” as a literal unnamed person; she has a sister (vs. 13). In Third John, he addresses a literal man, although named, Gaius. Either way, the message is clear.