The book of 3 John is a short letter in the New Testament of the Christian Bible, attributed to the Apostle John. It is addressed to a man named Gaius, commending him for his faithfulness and hospitality towards traveling Christian missionaries. The letter emphasizes the importance of supporting those who spread the message of Jesus Christ. In addition to praising Gaius, 3 John also criticizes a man named Diotrephes, who refuses to welcome these missionaries and seeks to assert authority over the church. The letter encourages believers to follow good examples and to remain steadfast in their faith and support for one another.