Many scholars believe that the author of 1 John also wrote 2 John at about the same time. Some believe that the two letters were sent together with 2 John acting as a “cover letter” and introduction for 1 John. Notice how 2 John echoes 1 John.
Verse 1 the recipient is not named and perhaps then, well known. “Her children” would be members of her church. Notice this reference to a woman church leader.
What is the “truth” the author refers to? Remember the content of 1 John also. As in 1 John there is concern over false teaching. In the ancient world people believed listening to wrong teaching would lead to wrong behaviors/evil deeds.
3 John: This is the only one of the three “John” letters addressed to an individual. Some scholars think 3 John is a letter of recommendation for the letter carrier.Demetrius is probably the bearer of these letters and possibly a missionary. This is a personal letter, addressed to Gaius. The names in the letter are Greco-Roman names, suggesting that gentiles were a part of these Johannine communities. All we know about Gaius is contained in this letter. Because he has extended hospitality to messengers (v5-6) scholars suspect he was the head of a household.
Read More About It
Culpepper, R. Alan “1,2,3 John” in HarperCollins Bible Commentary, rev. ed.James L Mays, ed. (New York: Society of Bible Literature) 2000.
Johnson, Luke Timothy, The Writings of the New Testament: An Interpretation, rev. ed. (Minneapolis:Fortress Press) 1999. Chapter 25, “1,2, and 3 John
Miller, Donald G.; Pheme Perkins “2 John”, “3 John” in The New Oxford Annotated Bible, Bruce M. Metzger, Roland E. Murphy eds. (New York: Oxford University Press) 1994.