Traditionally, the authorship of 1, 2, and 3 John has been ascribed to the apostle, John son of Zebedee, who also was understood to be the author of the Gospel of John and Revelation. Many contemporary biblical scholars believe that the writer of the letters was not the author of the Gospel. Rather, the letters are the work of a later community near the end of the first century that knew John’s Gospel well and were addressing issues that came up in their own community.
These three books are often referred to as letters, though only 1 and 2 John truly fit that description. 1 John has no addressee and reads more like an essay than a letter. The three books share the same writing style, however, and so are likely from the same hand.
2 and 3 John are the two of the shortest books in the New Testament. Both of these letters deal with particular problems faced by this community. In 2 John, the issue was maintaining the truth in the face of “deceivers” who were spreading their message that Christ has not come in the flesh. Such teacher should not to be welcomed into believer’s homes. 3 John mentions hospitality toward fellow workers, even if they are strangers, and the destructive impact of Diotrephes who refuses to do so.
I John, because it is more of a theological essay, shows significant overlap with the Gospel of John in respect to wording and concepts, some of which are also reflected in 1 and 2 John. For example: light vs. darkness; new and old commandments; loving other believers; Christ sent into the world because of God’s love; abiding in Christ; Christ laying down his life for others.
Lying in the background of these three books is the ancient heresy of Gnosticism, which taught, among other things, that the material body is evil and that the spirit is good. Hence, salvation was escape from the body through a special knowledge given only to those who are enlightened (Gnosticism comes from the Greek word gnosis, knowledge). Therefore, Christians who were influenced by Gnosticism did not accept that Christ was God in human form. Also, since the body was evil, some concluded that it had to be treated harshly through ascetic practices. Others came to the opposite conclusion: since the body is of no consequence, one can do as one pleases.
We have in these books, therefore, a glimpse into an early challenge to the gospel and how that challenge was addressed. The message of these books, however, is hardly limited to that context, particularly in its stress on the love of God and the love of Christians for one another.
– Peter Enns