That Jain metaphysics treats motion and rest as requiring their own distinct substances, dharma and adharma, rather than analyzing motion as a change of place, is unusual enough that a brief comparison with how other traditions handled the problem clarifies what the Jain move accomplishes.
Aristotle, addressing a similar problem, argued that place (topos) is itself something real, not merely a relation between bodies, because motion needs somewhere to occur and something to be relative to; but he located this requirement in place and in a hierarchy of natural motions proper to each element rather than positing a separate substance whose function is to enable motion, and had no counterpart to a substance enabling rest.
Nineteenth-century physics faced a comparable problem: needing a medium through which light waves could propagate, physicists posited the luminiferous ether, a substance filling all space whose sole function was to make wave propagation possible, abandoned once Einstein's special relativity showed propagation did not require one. The comparison is instructive because it fails informatively: the ether was posited to solve an empirical problem and was falsifiable and discarded, whereas dharma and adharma were posited within a metaphysical scheme not answerable to observation, to solve a structural puzzle, why an otherwise unbounded universe of souls and matter has a definite, bounded shape, the loka, with liberated souls rising to a fixed summit rather than ascending forever.
The Jain solution is therefore best understood not as primitive physics but as a metaphysical answer to a cosmological question, why the universe has an edge at all, a question most other traditions either answer differently or do not pose in the same terms.