it is an old saying.
mind could not be emptied but can be filled with knowledge.we treat minds as fire then when a fire is kindled with necessary fuel ,it serves as a purpose. it creates energy and heat.
this saying is totally meant for present situation.teachers should not fill the minds of children with excess of knowledge.according to the age the children the teacher should teach the studies limitedly.
thus when u light a fire it keeps on researching.