Revelation 2 discusses the messengers or angels of seven churches in Asia. What about churches not in Asia?

The book of Revelation was "to the seven churches which are in Asia" (1:4), and those seven churches are named in 1:11. Similarly, the book of Romans was addressed "to all who are in Rome, beloved of God, called to be saints" (Rom 1:7), and 1 and 2 Corinthians was to "the church of God which is at Corinth" (1 Cor 1:2; 2 Cor 1:1). While books to the Roman and Corinthian believers addressed specific issues that members of these churches were dealing with at the time, these books were copied, shared, and preserved by early Christians because they recognized that the local problems were addressed in the light of universal truth—so all followers of Jesus can learn from them.

The same is true of the book of Revelation. The letters (mini-epistles) to the seven churches address issues specifically relevant to those churches at that time, but, like other New Testament epistles, the exhortations and warnings found in the seven letters have universal truths in the backdrop. The mini-epistles and the entire book carry powerful lessons for all believers of all times. That's why each mini-epistle urges, "He who has an ear, let him hear what the Spirit says to the churches."