"As for the mystery of the seven stars that you saw in my right hand, and the seven golden lampstands, the seven stars are the angels of the seven churches, and the seven lampstands are the seven churches." (Revelation 1:20)
The Book of Revelation is apocalyptic literature, which means that it contains many highly symbolic elements. This is distinct from historical narrative in that most of the details are to be taken literally. The author expresses himself in a way similar to Old Testament writers such as Daniel and Ezekiel. John wrote to the people of Asia Minor in regard to how God was at work in their day and also how He will work to bring things to a glorious end. Chapters two and three of Revelation contain words of Jesus commending the good deeds of the seven churches as well as Him reproving their error, calling them to repentance.
The passage is unclear as to who precisely the seven “angels” of the seven churches are. Some believe them to be angels appointed by God to act on behalf of the churches. This view would be comparable to what we see in Daniel in which angels represent nations (Daniel 10:13-21). Another point of view in regard to the seven angels is that they are messengers who delivered John's scroll to the churches to be read. That pattern of behavior is not without precedent in Jewish history (1 Maccabees 1:44). A third interpretation as to the identity of the seven angels is that they are bishops, but it would not be wise to put much weight on a debatable text like this one in the context of episcopal development.
The first view outlined in the previous paragraph seems to more reasonably fit the context of Revelation 1:20 than others. In Revelation, the term "angel" is always a reference to heavenly beings rather than human messengers. That term has the same meaning elsewhere in apocalyptic literature. Angels were portrayed as stars (Isaiah 24:21; 2 Baruch 51:7-11). This may mean that God has given the responsibility of churches to angels, although we cannot speak dogmatically. We know that there is a time in which believers will judge angels (1 Corinthians 6:2-3). The church has been commissioned by God to provide witness for Jesus.
Even if the seven angels in Revelation 1:20 were a reference to bishops, the New Testament does not demand a specific structure of leadership in the church. In other words, while churches are seen to be governed by pluralities of elders (Acts 14:23), this idea is not applied in a strict or exhaustive manner. Consequently, there are acceptable differences in how church government can be arranged. A church could temporarily assign a role of first among equals to one elder for the sake of convenience in resolving matters. That in and of itself is not a problem.