Brahma, Vishnu and Shiva, are the "All existing and permuting" triad. That is a spiritual concept. Brahma, exists everywhere and is the Akasha, Aether. Shiva, is "That which is not", potentiality, but is also related to the invisible fire. Vinsu is the maintainer, or the solidifier of states between the two. Shiva is the destructive but the life force at the very same time.
Shiva is also related to the active principle in nature which in creation is extremely important and without which, life cannot exist. If something is active, without Vishnu and Brahman, it cannot sustain, therefore, Shiva is the God of destruction as well as the central figure. This is like electricity which has to flow through a circuit and maintained, and gives light. The same cause that can make light die, which makes it most important, is at the same time the very cause of it's creation and maintenance. Shiva in this case becomes the one who is all and nothing at the same time, which is why they call him "That which is not" and at the same time the creative spark.
Shiva is rightfully getting the highest worship, Shiva is the principle of the spark of existence.