The essentia of a thing is the essence of that thing. The essence is every thing that the thing is made of, it’s truest compound and make. Without the essentia there is nothing essential about that thing, the essential helps everything around or outside of that thing know what the thing is all about. (I’m using the term thing a lot), but you will only know about something after you have gotten to its core. And find out what is it good for, hopefully something good. The essential nature of something is also it’s quentessential or Qi (Chee) its strength and fortitude… more later.