I have created this page to explain the references to bishops, which are necessary all over this site. It's important that you know what was meant by the term in early Christianity.
This page grew to include too much information. That information is useful, but many of you are just looking for a brief explanation of what a bishop was in the early church. Here it is. If you need further explanation or verification of anything said in the brief overview, it is certain to be covered in the rest of the page.
In Scripture, bishops and elders are interchangeable terms. It is clear that Paul and Peter's churches were led by a group of elders (older, experienced, or trusted men), whose office was referred to as bishop or overseer (interchangeable terms, both translate the one Greek word episkopos).
It was their job to shepherd the church (Acts 20:28), and so they are the "pastors" in the New Testament.
Apparently, from history, John did not format his churches this way. He had a group of elders, but only one of those held the title of bishop or overseer. He was, so to speak, the head elder or head pastor.
Sometime during the 2nd century, John's usage won out. There is no reference to bishops and elders being the same people after Polycarp's letter to the Philippians dated some time between A.D. 110 and 150.
The later reference to priests is a reference to the elders, who began to be called priests around the mid 3rd century.
Deacon is simply the Greek word diakonos left untranslated. The word is found all over the New Testament, over 30 times, and it is translated servant except in 1 Tim. 3.
It should have been translated servant there as well. The office should not have some mysterious Greek title, "deacon," but it should simply be "servant."
In the 2nd century churches servants (or deacons, if you must) visited the sick, helped with whatever was needed during services, and brought communion bread and wine to those who could not attend Sunday meetings, whether due to sickness or imprisonment.
Interestingly, in the 3rd century, there is reference to them watching the doors to make sure only Christians entered the meeting.
If you'd like, you can see a much more thorough treatment of the history of these offices.