Change happens either in Form (appearance available to our five senses) or Essence (Content, Purpose, Function). Form can be deceiving if its Essence is not taken into account. Understanding something in totality its essence and form with its relations and its treatment as a process is necessary.
For example; the shaving machine and razor are different things in Form but the same in essence, that is, function.
Likewise, to be a slave in essence is to be forced to work just as to be a master is to live on someone else's labour. Slave, serf, and wage slave are different in names and Forms but the same in Essence. One is forced by the whip, law of the land, or circumstantial coercion to work for someone and that someone makes a profit from his labour. The social relation remains the same in essence.