Full Idea
We proved that there cannot be an infinite magnitude, and that it is impossible for something finite to have infinite power, but the first agent of movement causes eternal movement for an infinite time, so it must be indivisible and have no parts or size.
Gist of Idea
The source of all movement must be indivisible and have no magnitude
Source
Aristotle (Physics [c.337 BCE], 267b19)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.231
A Reaction
Note that Aristotle is already attributing 'infinite power' to this special thing. It is more than just a first domino to fall over. Its having no size quickly takes it outside of space, and makes it a 'spirit'. We are watching the construction of God.