The Number Seven

Revelation 1:11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send [it] unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea.

The names of the seven churches are symbolic of the church in different periods of the Christian Era. The number 7 indicates completeness, and is symbolic of the fact that the messages extend to the end of time, while the symbols used reveal the condition of the church at different periods in the history of the world.
{AA 585.3}