All matter moves because there is no uniquely stationary refence frame. Thus if you move with an object its speed as measured in your framework is zero. If you move relative to the same object, you will think it is moving and you will measure a speed relative to your framework. The maximum upper limit to the speed you can measure is thus given by the speed of light. As I said it is the upper limit because matter (including you the observer) can never move with this speed relative to any other piece of matter in the universe. Why do they move? As said above there is no stationary reference frame in the universe; so matter must always move relative to each other! If they did not, one would have a uniquely stionary reference frame.

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