Hello,
I would also like to note that '666' represents the 'Holy Grail' or in other words our Solar Plexus Chakra that is ruled by the Sun.
Basically, in other words, it represents where our 'Life Force' is located, because for example, in black magick, if you attack somebody's Solar Plexus Chakra repeatedly, or program a thoughtform (that you create) to attack it, that person can actually die.
No other chakra holds such position, every other chakra rules different things, but the Solar Plexus Chakra rules our Life Force.
It's where we get our motivation, life, 'immortality' stored. By 'immortality', I am referring to what the 'Holy Grail' represents, or the 'Fountain of Youth'.
If I have made any mistake, please do point them out, I was only referring to the things I understood from the Joy of Satan Website.
Thank you.
HAIL SATAN!