In Number system, for any positive number, there is a corresponding negative number. what is the sum of all numbers. Zero ?
Also have you wonder there can not be positive without negative, and viceversa. Though look like enemies, Without one, the other can not live! But zero lives all by its own.
Wei Wu Wei, In his "Ask the Awakened " explains void as given below:
"The Void is not of the nature of a black abyss or a bottomless pit. Rather is its nature 'vast and expansive like space itself'. It is apprehended as 'serene, marvelous, all-pure, brilliant and all-inclusive'. Above all does it partake of the nature of light. And it is not anything. For Void is Mind Itself, and Mind Itself is Void".