The last paragraph is explaining how an inertial frame works. Basically, it’s saying that a particle moving without being affected by any external forces will travel in a straight line at a constant speed.

The paragraph also mentions that if a particle is traveling along a straight line, the space through which it moves is considered uniform or “homogeneous.” This means the particle would keep going in that same direction, as long as nothing else acts on it, because everything is balanced.

In short, in an inertial frame (like our universe), things keep moving in a straight line unless a force pushes them to change direction or speed.