Pastor Rit covers 3 John, which is a personal letter from the Apostle John to Gaius. In this letter, the Apostle John rejoices that he's heard great reports from others of Gaius' faith and his service to the Church. The Apostle John informs Gaius of another leader in the church, Diotrephes, and his evil deeds. The Apostle John ends his letter praising Demetrius for his good testimony.
We see in this Epistle that the Apostle John was not slack in naming someone who is teaching heresy and harming the Church.