There are separate opinions of who the Angels of the Seven Churches were I will provide the differing explanations A&B.
A Angels of the Seven Churches
It is evident from the contexts of the various Biblical passages in which the word “angel” appears, that the word does not always represent the same idea. In such passages as Dan_12:1 and Act_12:15 it would seem that the angel was generally regarded as a superhuman being whose duty it was to guard a nation or an individual. However, in Mal_2:7 and Mal_3:1 (Hebrew) the word is clearly used to represent men. In the New Testament also, there are passages, such as Jas_2:25 (Greek), in which the word seems to be applied to men. The seven angels of the seven churches (Rev_1:20) received seven letters, figurative letters, and therefore it would seem that the seven angels are also figurative and may refer to the seven bishops who presided over the seven churches of Asia. Or the angels may be regarded as the personifications of the churches.
B ANGELS OF THE SEVEN CHURCHES
1. According to one set of opinions, these angels were men, and the majority of writers have held them to be (1) the presiding presbyters or bishops of their respective churches. But while this view is attractive and popular, the reasons against it are strong. Human officials could hardly be made responsible for their churches as these angels are. A bishop might be called an angel, i.e. a messenger, of God or of Christ (cf. Hag_1:13, Mal_2:7, 2Co_5:20), but would he be called ‘the angel of the church’? Above all, it is certain that at the early date to which the Apocalypse is now generally assigned a settled episcopate was unknown. (2) Others have supposed that the angels were congregational representatives, church messengers or deputies (which would be in harmony with the proper meaning of the word ‘angel’), or even the person who acted as ‘Reader’ to the assembled church (notice ‘he that readeth’ in Rev_1:3). But if the responsibility put upon the angels is too great for bishops, it is much too great for any lesser functionaries. Besides, the glory and dignity assigned to them as the stars of the churches (Rev_1:20) is inconsistent with a position like that of a mere Reader or deputy.
2. A good many have held that ‘angels’ is to be understood in its ordinary Scriptural application, not to men, but to celestial beings. In support of this are—(1) the fact that throughout the rest of the book the Gr. word, which is of very frequent occurrence, is invariably used in this sense; (2) our Lord’s utterance in Mat_18:10, which suggests a doctrine of angelic guardianship; (3) the fact that in Daniel, to which the Apocalypse is so closely related, the guardianship of angels is extended to nations (Dan_12:1). The objections, however, are serious. No definite Scriptural teaching can be adduced in favor of the idea that churches have their guardian-angels. Messages intended for churches would hardly be addressed to celestial beings. Moreover, it is scarcely conceivable that such beings would be identified with particular churches in all their infidelities and shortcomings and transgressions, as these angels are (see, e.g., Dan_3:1; Dan_3:15 ).
3. The most probable view, accordingly, is that the angels are personifications of their churches—not actual persons either on earth or in heaven, but ideal representatives. It is the church, of course, that receives the letter, the ‘Thou’ of address having manifestly a collective force, and it is to the church itself that the letter is sent (cf. Rev_1:11, where there is no mention of the angels). The idea of angels was suggested, no doubt, by the later Jewish beliefs on the subject, but it is used in a figurative manner which suits the whole figurative treatment, where the glorified Jesus walks among the golden candlesticks, and sends to the churches messages that are couched in highly metaphorical language. It might seem to be against this ideal view that the seven churches, as candlesticks, are definitely distinguished from the seven angels, as stars (Rev_1:12; Rev_1:16; Rev_1:20). But it is quite in keeping with the inevitable distinction between an actual and an ideal church that they should be thus contrasted as a lamp and a star.
A. International Standard Bible Encyclopedia
B. Hastings Dictionary of the Bible