2 Cents

none of the language in the book is meant to be taken literally.

One of the more interesting ways John uses symbols is the way in which he employs numbers to communicate various truths.

In the book of Revelation you will see abundant uses of the numbers 3, 4, 6, 7, 8, 10, and 12.  You will also see multiples of these used as well (i.e. the 144,000 in ch. 7).

With extensive help from commentators Christopher Davis and G.K. Beale, here is an explanation of the typical meanings behind John's symbolic numbers.

TWO - The number of valid witnesses required to establish a matter.  Its roots can be found in Deut. 19:15.  

THREE - The number of God, who is a Trinity: Father, Son, and Holy Spirit.  This also has OT roots in Isaiah 6:3 where God is worshiped as "Holy(1), holy(2), holy(3)," a phrase that is repeated in Rev. 4:8. 

FOUR - The number for the world or God's creation.  Common biblical references include the "four corners of the earth" (Ezek. 7:2; Rev. 7:1), and the "four winds" (Jer. 49:36; Ezek. 7:9; Dan. 7:2).  We also see the four directions north, south, east, west used to refer to the entirety of God's creation (Gen. 28:14; Luke 13:29).  

SIX - One less than seven (see below).  Used of something that does not measure up or is incomplete in power or effectiveness.  It is often used of evil powers in Revelation (666), which communicates their weakness compared to God and his people.  

SEVEN - The number of fullness, completion, and perfection.  Sometimes it can be used to describe evil, in which case it would mean complete or full evil.  Most of the time it is used to describe good.  Origins for the symbolic meaning of seven can be traced to the seven days of creation making a full week in Gen. 1-2. 

EIGHT - Symbolizes Jesus Christ. 

TEN - Can be used to represent completeness.  Often it represents the idea that God has set limits to whatever 10 is describing.  Conversely 1000 (10x10) refers to limitlessness.   

TWELVE - Represents the people of God - those who love him and serve him faithfully and do not give  up their faith in the face of suffering and persecution.  It's roots can be traced back to the 12 tribes of Israel in Genesis as well as the 12 Apostles.