In the Bible, in general the number 7 is pointing to (the good) God and the number 6 is pointing to (the wicked) man.

Also read this article on biblical numerology.

Throughout the Bible, God often gives symbolic significance to mundane items or concepts. For example, in Genesis 9:12–16, God makes the rainbow the sign of His promise to Noah (and, by extension, to all mankind) that He will not flood the whole earth again. God uses bread as a representation of His presence with His people (Numbers 4:7); of the gift of eternal life (John 6:35); and of the broken body of Christ, sacrificed for our sins (Matthew 26:26). 

The number six appears throughout Scripture and is most commonly connected with mankind and human activity. Humanity was created on the sixth day of creation (Genesis 1:26–31), and people were commanded to labor for six days before resting on the seventh (Exodus 20:9–11). Because seven is often associated with completion or fullness, six can sometimes represent what is incomplete, falling short, or merely human.