John writes 1, 2, and 3 John
1 John 1:1–4; 2 John 1:1; 3 John 1:1
John wrote to churches in Asia shaken by false teachers who denied that Christ had come in the flesh, assuring believers that they could know they had eternal life, and calling them to love one another.
He who doesn’t love doesn’t know God, for God is love.
1 John 4:8 (World English Bible)
The first letter opens with John's testimony as an eyewitness: what he had heard, seen, and touched of the Word of life (1 John 1:1). The two short letters, from “the elder,” deal with hospitality and false teachers.
Dating notes
About AD 90–95, from Ephesus. The date is an estimate; Scripture doesn't say when the book was written.