Then something has been at work to start cosmic activity in certain areas while passing over others in which the raw material is equally available.

What is this something?
At first we might be inclined to attribute the development of cosmic energy to the etheric particles themselves, but a little consideration will show us that this is mathematically impossible in a medium which is equally distributed throughout space, for all its particles are in equilibrium and so no one particle possesses _per se_ a greater power of originating motion than any other.

Consequently the initial movement must be started by something which, though it works on and through the particles of the primary substance, is not those particles themselves.

It is this "Something" which we mean when we speak of "Spirit." Then since Spirit starts the condensation of the primary substance into concrete aggregation, and also does this in certain areas to the exclusion of others, we cannot avoid attributing to Spirit the power of Selection and of taking an Initiative on its own account.
Here, then, we find the _initial_ Polarity of Universal Spirit and Universal Substance, each being the complementary of the other, and out of this relation all subsequent evolution proceeds.

Being complementary means that each supplies what is wanting in the other, and that the two together thus make complete wholeness.