Essence
True Nature, Substance, Reality
noun, の adjective
The real quality of something is its essence, or its true nature. Whether it's good or bad is a different story.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
人間の本質って、何だろうね。
What is the essence of humanity, I wonder?
問題の本質の追求って難しいよね。
Pursuing the essence of a problem is difficult, isn't it?
この男は、物事の本質を見抜くことができる。
This man has the ability to instantly perceive the true nature of anything.