Newton conceived space as being:
Absolute space, in its own nature, without regard to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces; which our senses determine by its position to bodies: and which is vulgarly taken for immovable space
and motion as
Absolute motion is the translation of a body from one absolute place into another: and relative motion, the translation from one relative place into another
But space has no point of origin, each point is alike as another. So no motion can be absolute, every motion must be relative.
Introduce a particle into this space. Then this particle cannot be at rest. For what would it be at rest with? Here I do not mean with another particle, but with regards to space itself.
From this is it possible to deduce that a particle moves in a straight line linearly?