"As no outward motion or change, when normal, in man's external body can take place unless provoked by an inward impulse, given through one of the three functions named, so with the external or manifested Universe"

This quote by H. P. Blavatsky is recommending that the external universe is similar to the body in that it is driven by an inward impulse. Simply as an outside motion or change in the human body can not occur without an inward impulse, the very same is true for the external universe. This inward impulse is given through among the three functions: thought, sensation, and will. Blavatsky is suggesting that the external universe is driven by the very same forces that drive the body, which these forces are the very same for both the internal and external worlds. This quote is a pointer that the external universe is not separate from the internal world, but rather is linked and driven by the exact same forces.