This is also a brief letter of Apostle John.  There is no compelling reason to doubt the traditional view that apostle John wrote this letter.  It was addressed to John’s dear friend Gaius to encourage him in his walk with the Lord.  Most probably he was a convert of John's ministry. He was a hospitable and a spiritual leader in the church. On the other hand Diotrephes was self-seeking leader who sought dominance over other elders. Also Diotrephes  was refusing to support faithful servants of God. John encourages Gaius to be hospitable to God’s servants who are faithful.  Demetrius was a respected servant of God whom Diotrephes opposed. The loyalty to the truth and good testimony among believers are the test for supporting any ministry.