"The mystery of the seven stars which thou sawest in My right hand, and seven golden candlesticks. The seven stars are THE ANGELS of the seven churches: and the seven candlesticks, which thou sawest, are the seven churches." Revelation 1:20
The Bible does not use the term "church" to refer to any specific organization. The "church" in Revelation is the commandment-keeping, people of God (regardless of what religion they happen to be). Also, the number seven in Revelation is a symbol of perfection -not a literal number... See the Bible Prophecy study section for the texts behind these conclusions.