The number seven is the most frequently encountered number in the book of Revelation:
6 Seven as a number of completeness is also apparent from the seven days of creation in Genesis Gen. 1:1, which is the complete period of Gods work of creating.Gregory K. Beale, The Book of Revelation: A Commentary on the Greek Text (Grand Rapids, MI: William B. Eerdmans Publishing Co., 1999), 58.
8 Other examples of completeness are the seven seals, seven trumpets, and seven bowls, which are so numbered in order to underscore the completeness of Gods worldwide judgment and salvation.Beale, The Book of Revelation: A Commentary on the Greek Text, 59.
9 Although some restrict this warning to the book of Revelation only, it seems significant that no other NT book closes with a warning even remotely similar.
12 God completed His mighty work of creating, constructing, and energizing the entire cosmos and all its creatures in the very first seven-day period of history. Because of sin and the curse, He has since been accomplishing His might work of redeeming and saving the creation. One day this work also will be completed.Morris, The Revelation Record, 31.