A good brother asked me this question, and below is my answer to him:

To the angel of the church in Ephesus write (Revelation 2:1).

There is certainly a variety of opinions on this very question. Nevertheless, whatever one's view with respect to the meaning of "angel" or "messenger," clearly the content of each message was directed to the whole church in each of the seven cities of Asia Minor.

For me, the simplest view is to read it literally as a reference to angels. This is the most common understanding and use of the Greek word angelos in the NT, as well as the Greek OT. Also, aside from these perhaps disputable references, it is always used as such in the Book of Revelation. If John is exiled on Patmos, I daresay communication was somewhat restricted. Perhaps he had visitors from these seven churches or even sent for them; however, it seems more likely that John was privileged to record in his scroll (the Book of Revelation) the message God was sending through angelic witnesses to these churches. In light of the far more dramatic revelations John experienced in the composition of Revelation, this does not seem incredible to me. The words "to the angel of the church" may suggest either that these angels were assigned to particular churches or else they were the guardian angels over those churches. This latter case is certainly not farfetched in view of what we learn from the prophet Daniel, where angels and demons are shown to have some power over nations and rulers.

 

What is more in Revelation 1:20 these "angels" are also called "stars."

 

The seven stars are the angels of the seven churches.

 

When stars are used symbolically and not literally as stars in the sky, they often represent angels, even fallen ones (cf. Revelation 9:1; 12:4).

 

Therefore, John was probably writing to literal angels in Revelation 3-4.