3 was the symbol for God.
6 was the symbol for Man.
666 is Man becoming God.
God only exists in the minds of those who believe in him. As our society advances technology we will come to believe in science fact, rather than faith. So eventually God will be dead and the world will be a better place.
To bad we will not be alive to see that happen. We created God because we feel the world revolves around ourselves. We refuse to believe that when we die we become nothing... and life still exists. How can life exist when you're dead, YOU are the center of the universe. Right?
