Full Idea
In the absence of a mover and a moved there's no such thing as motion, and mover and moved cannot possibly be uniform with each other. It follows that we should always associate rest with uniformity and attribute motion to diversity.
Gist of Idea
Motion needs differing moved and mover, so it originates in diversity
Source
Plato (Timaeus [c.362 BCE], 57e)
Book Reference
Plato: 'Timaeus and Critias', ed/tr. Waterfield,Robin [OUP 2008], p.53
A Reaction
Newtonian inertia allows movement without a mover. Perhaps Plato means acceleration rather than movement. Newton ignores the question of what got the inertial movement started. The full picture needs powers!