The Third Book of John is the third-to-last book of the New Testament and the Christian Bible as a whole, and attributed to John the Evangelist, traditionally thought to be the author of the Gospel of John and the other two epistles of John. The Third Epistle of John is a personal letter sent by "the elder" to a man named Gaius, recommending to him a group of Christians led by Demetrius, which had come to preach the gospel in the area where Gaius lived. The purpose of the letter is to encourage and strengthen Gaius, and to warn him against Diotrephes, who refuses to cooperate with the author of the letter.