Revelation 1-3 (The Daily Walk Bible).
I think that the letters to the seven churches were written to confront specific issues in each church, but that the messages are timeless. Additionally, the book would have been brought to each church and read there, so they would all know the good and bad about each other. So, what do we learn for us today? I think we find seven characteristics that we should try to have as churches (and even individuals): Ephesus teaches us that we should be loving, Smyrna that we need confidence, Pergamos teaches the importance of sound teaching, Thyatira shows the necessity of godly leadership, Sardis that we should be spiritual, Philadelphia reminds us of the need to be faithful, and Laodicea shows us that we need to be humble.
And did you catch that vision of Jesus in chapter one? Wow!