The Early Church (Excluding Paul and Acts)

James 

James was probably written by James, the brother of Jesus, and leader of the Jerusalem council (Acts 15). The letter is addressed to the "twelve tribes scattered among the nations" (1:1), probably meaning Jewish Christians of the diaspora who predominantly comprised the church at the time. "As leader of the Jerusalem church [council], James wrote as pastor the to instruct and encourage his dispersed people in the face of their difficulties" (NIV Study Bible: Introduction to James).

James

- 2:2 - if there should come into your assembly...  

- 3:1 - My brethren, let not many of you become teachers...

- 5:14 - ‭Is anyone among you sick? Let him call for the elders of the church...

The early church was the assembly of Christians. It contained teachers and had elders (plural).

1 Peter

The author identified himself as the apostle Peter. The letter was written to Jewish and Gentile Christians (churches) scattered throughout Asia Minor. The letter was written for the purpose of "exhorting and testifying that this is the true grace of God in which you stand" ‭(I Peter 5:12), "true grace" being the enablement of Christians to suffer for Jesus. 

- ‭I Peter 3:21 - There is also an antitype which now saves us—baptism (not the removal of the filth of the flesh, but the answer of a good conscience toward God), through the resurrection of Jesus Christ, 

- ‭I Peter 5:1-3 - [1] The elders who are among you I exhort, I who am a fellow elder and a witness of the sufferings of Christ, and also a partaker of the glory that will be revealed: [2] Shepherd [pastor] the flock of God which is among you, serving as overseers, not by compulsion but willingly, not for dishonest gain but eagerly; [3] nor as being lords over those entrusted to you, but being examples to the flock...

Baptism is an antitype of the flood, and is important for salvation. Jesus commanded His disciples to be baptized, and we see in Acts that converts were immediately baptized. It is not baptism that saves, but Jesus through His resurrection. Elders were among those who Peter wrote to, and He himself was an elder. The elders were to shepherd, or pastor the flock who were among them. They were the overseers of the flock, and were to serve willingly, not by compulsion, making it seem evident that being an elder was not a very desired position, as it is in the western church of today. Elders were to serve as an example to the flock.

2 John and 3 John

2 John and 3 John were written by the apostle John. In both letters, John begins by referring to himself as "The Elder", indicating that he was an elder of the church. Scholars believe that he may have served as an elder of the church of Ephesus.

2 John was written to "the chosen lady and her children", being either an unknown Christian woman and her children in the  province of Asia, or more likely the church and its members. The purpose of the letter is to warn the church of deceivers and antichrists who have "gone out into the world", indicating that they were in the church, and to not be deceieved, but to remain in the teachings of Christ. John warned them not to allow these teachers into their homes or welcome them, because if they do, they share in their wicked work. 

3 John was written to his "dear friend Gaius", to commend his faithfulness to the brothers in one of the churches in the province of Asia, and to inform him of Diotrephese who rejected John and the church. John was hoping to personally go to the church to call attention to what he was doing, and to bring correction.

- 2 John 1:1 - [1] The Elder, To the elect lady and her children...

- 3 John 1:1 - [1] The Elder...