All bodies do not resist a change in their state of motion to the same extent. Some resist more than others. For example, if we give a hard kick to a football it flies off. But if we kick a stone of the same size with the same force, it may not move at all, rather we would injure ourselves. This is because the inertia of the stone is much more than that of the football. Hence more massive the object, greater will be the inertia.