Motion and rest are not absolute because they are relative concepts. The perception of motion or rest depends on the observer's frame of reference.
According to the theory of relativity, there is no absolute frame of reference in the universe. This means that there is no preferred or special frame from which all motion can be measured. Instead, any observer moving at a constant velocity can consider themselves at rest and describe other objects or observers as moving relative to their frame of reference.
For example, if you are sitting on a train moving at a constant velocity, you may perceive yourself as being at rest. From your perspective, objects inside the train also appear to be at rest or moving with the same velocity as the train. However, an observer standing outside the train sees both you and the train in motion. The perception of motion or rest differs between the two observers due to their different frames of reference.
The principle of relativity states that the laws of physics should be the same in all inertial reference frames. Inertial reference frames are frames of reference in which an observer moves with a constant velocity or remains at rest. This principle is supported by experimental evidence and has been confirmed in numerous experiments.
In summary, motion and rest are not absolute because they depend on the observer's frame of reference. Different observers may perceive an object as moving or at rest based on their relative motion, and there is no privileged or absolute reference frame from which all motion can be measured.