3 John 1:1-14
The second epistle commanded that those who do not bring "the doctrine of Christ" should not be received. The third epistle urges believers to receive and help those who do teach it (cf. John 13:20). Caring for the Lord’s servants is one way of being involved in Gospel work (v. 8).
Several people are introduced to us in this short letter. Gaius, to whom the letter was addressed, was a beloved friend whose soul was prospering; he was walking in the truth, he was acting faithfully and his love was well known amongst the people. There is also a good report about Demetrius who is mentioned later on (1 Timothy 3:7). By contrast, in the same assembly was a man called Diotrephes who loved to be the top man (1 Peter 5:3), said nasty things about the apostle, refused to receive the brethren and put others out of the assembly. John also mentions fellow evangelists who had gone forth "for his Name’s sake" (v. 7; see Acts 5:41). The Name which is above all others is that of Jesus: He alone was their message and the warrant for their mission (Acts 8:35).
The apostle urges that we "follow not that which is evil, but that which is good" v. 11; 1 Thessalonians 5:15). We find examples of good and evil both in this epistle and also around us. Which do we follow? Above all else let us follow the Lord Jesus, in whom only good was ever found (Mark 7:37).