John tells us of two men.
He was beloved.
He had made the truth of Jesus his truth.
He walked in the truth of Jesus.
It caused him to befriend and offer hospitality to strangers.
He helped and supported those who were proclaiming the good news of Jesus.
Loved to be first instead of being a servant.
He did not accept the words of an apostle of Jesus.
He also unjustly accused John with wicked words.
He did not receive the brethren who went out to teach the good news of Jesus.
Not only did he not receive them, he forbade any in the church from receiving them as well.
He would even put out of the church those who would help those teachers.
After informing Gaius of the actions of Diotrephes, John gives this warning:
“Beloved, do not imitate what is evil, but what is good. The one who does good is of God; the one who does evil has not seen God.”