Why, they say the movement of the body, is it necessary to indicate with respect to which bodies

Why, they say the movement of the body, is it necessary to indicate with respect to which bodies this movement takes place?

Any movement is relative. This means that depending on which reporting system we choose, the body can either move or be at rest. As an example, consider the movement of an aircraft: if we take an airport dispatcher as the reporting system, then the plane is in motion (since it moves away from the dispatcher), and all formulas and laws act on its movement. However, if we choose the pilot of this aircraft for the reporting system, then the aircraft is at rest.

Therefore, when solving problems related to body movement, it is always necessary to indicate the point of the report.