The number 6 at times represents imperfection in the Bible.
A Philistine man of the Rephaim was of “extraordinary size,” and his “fingers and toes were in sixes.” (1 Chronicles 20:6)
King Nebuchadnezzar erected a golden image 6 cubits in breadth and 60 cubits high, to unify his political officials in one worship. When God’s servants refused to worship the image of gold, the king had them thrown into a fiery furnace. (Daniel 3:1-23)
The number six falls short of seven, which stands for completeness from God’s standpoint. Therefore, a triple six represents gross imperfection.
The number of “the wild beast” is 666 and is called “a man’s number,” indicating that it has to do with imperfect, fallen man, and it seems to symbolize the imperfection of that which is represented by “the wild beast.” The number six being emphasized to a third degree (the six appearing in the position of units, tens, and hundreds) therefore highlights the imperfection and deficiency of that which the beast represents, or pictures.—Re 13:18.
Certain numbers used in the Bible have symbolic meanings, but only within the context of the Scriptures in which they are used.
For example, the number four is used to denote allness or universalness. This idea is conveyed in such expressions as “four extremities of the earth” and “four winds of the heavens.” (Isaiah 11:12; Daniel 8:8)
When the number seven is used in a symbolic way, it represents completeness. (Leviticus 4:6; Hebrews 9:24-26) These and other symbolic numbers used in the Scriptures gain meaning from their prophetic context.
Although the Scriptures give a measure of importance to certain numbers, the Bible does not encourage us to link the letters of certain words with numbers to uncover mystical truths.