John must record what he sees because Revelation is an important message for the churches.
The angels (or messengers; Greek angelos) of the seven churches could be:
the guardian angels of these churches (compare Matthew 18:10; Acts 12:15);
the leading officials of the churches (compare Matthew 11:10, where “messenger” is angelos); or
a personification of the ethos (spirit or character) of the church.
The best understanding is probably a combination of 1 and 3.