WRITER, The apostle John. 
ADDRESSED, To Gaius
3Jo 1:1
KEY NOTE. Christian hospitality.
KEY VERSE
3Jo 1:8
SYNOPSIS. The subject-matter centres around three characters, Gaius, Diotrephes and Demetrius, and some itinerant evangelists.
I. Gaius, to whom the epistle was written.
(1) The identity of this man.
This cannot be positively determined. There are several persons by this name mentioned in the New Testament. The one spoken of by Paul,
Ro 16:23
may very likely be the same man to whom John writes but it is entirely uncertain.
(2) Characteristics of,
(a) Worthy of the affection of John
3Jo 1:1,2
(b) A consistent Christian, walking in the truth
3Jo 1:3,4
(c) Given to hospitality
3Jo 1:5,6
II. Diotrephes, apparently a leading man in the church.
(a) Ambitious and bigoted
3Jo 1:9
(b) Assuming to be an over-lord of the vineyard, will receive a merited rebuke from the apostle when he comes
3Jo 1:10
III. Demetrius, In contrast to Diotrephes, a model churchman of excellent reputation.
3Jo 1:12
IV. Christian evangelists.
(a) Itinerant spiritual labourers, rendering gratuitous service for Christ's sake
3Jo 1:7
(b) Worthy of hearty welcome and hospitality although bitterly opposed by the arrogant Diotrephes
3Jo 1:8-11
V. The closing salutation.
3Jo 1:13,14
(Outline from Thompson’s Chain Reference Bible)