Though never identified in the letters, the author of the Johannine letters is almost certainly the apostle John, the son of Zebedee, and author of the Gospel of John. Based on writing style, there is good reason to think the writer of Revelation is a different John. The John who wrote 1, 2, and 3 John was one of the inner circle of apostles and “the disciple whom Jesus loved” (John 13:23). Though he started his adult life a fisherman, he ends it as one of the pillars of the new, growing Christian church, a highly respected leader in the Ephesus area in particular.
The Johannine letters are likely some of the latest parts of the New Testament. Some date John’s letters to the late 80s. If this is correct, the first generation of those who had actually seen Jesus were dying and John was pure royalty. Given that no specific recipients are mentioned in 1 John, the first epistle was likely a circular letter distributed among a diverse group of Christians, especially in Asia Minor around Ephesus. Given the general nature of the teachings of the letter, that makes perfect sense. Second and Third John are equally as general and universal.
Most scholars situate the Johannine letters in the context of Gnosticism. This false version of Christianity really blossomed in the second century AD but it was likely an early version John was addressing. Gnosticism taught that the physical was evil and the spiritual was good. The fleshly body was wasting away and either an impediment to holiness or a temporary object of no consequence to be used and abused because only the soul really mattered. Gnosticism derives its name from the Greek word “gnosis” which means “knowledge,” because the truly spiritually enlightened ones have a special knowledge that sets them apart from their more earthbound peers. With these beliefs, a good Gnostic could not believe Jesus was fully human and flesh. One version of Gnosticism called “doceticism” taught that Jesus only seemed to be flesh and another version called “Cerinthianism” taught that the man named Jesus gained his spiritual nature at baptism and lost it before he died. We will hear John attacking this sort of thinking in his letters, 1 John especially. As the flesh was evil, one was supposed to either deny his fleshly desires through asceticism (seen earlier in Colossians) or indulge the flesh in licentiousness. This latter version seems to be the one John addresses.
John wrote 1 John to expose false teaching and counter any wrong thinking about Jesus that had cropped up. As one of the last eyewitnesses of Jesus, John could testify that Jesus was indeed flesh. John also believed that the libertine worldliness of pre-Gnostic Christianity was eroding the true Christian witness. In 2 and 3 John, John encourages faithful Christians to extend hospitality to evangelists he would have sent out even if powerful, possibly-Gnostic leaders in his church opposed him.