First Epistle of John

The First Epistle of John is the sixty-second book in the Christian Bible, and the twenty-third in the New Testament.
This book is believed to a letter from John.
There is some disagreement over whether the John who wrote the letters of John, the John who wrote The Gospel of John, and the John who wrote the Book of Revelation are the same person.
This letter was probably written in Ephesus in AD 95–110. It was written to show that Jesus really came "in the flesh", and not only as a spirit, as some false teachers were saying. John says they are "anti-Christ", meaning against Christ. This false teaching is known as docetism. It says that Jesus only seemed to be a human person with a real body. John's letter says that Christians can tell if teachers are true. True teachers will say that say that Jesus came in the flesh. True teachers are also known by their ethics, and by their love.
John wrote the letter so that the joy of his readers would "be full" (Chapter 1, verse 4).
Also he says that as true Christians they would "not practice sin" (keep sinning) (Chapter 2, verse 1); that "we should love one another" (Chapter 3, verse 11); and that "you who believe in the name of the Son of God... may know that you have eternal life." (Chapter 5, verse 13). So we see that the aim of the letter was to make the Christians more full of joy, and also to help readers to know if they are really saved.