The Essential is Invisible to the Eye

"Now, here is my secret, a ver simple secret. It is only with the heart that one can see rightly; what is essential is invisible to the eye."
From The Little Prince, by Antoine de Saint-Exupéry

"A symbol is indeed the only possible expression of some invisible essence, a transparent lamp about a spiritual flame; while allegory is one of many possible representations of an embodied thing, or familiar principle, and belongs to fancy and not to imagination: the one is a revelation, the other an amusement."
William Yeats

"You are eternal, and the invisible essence of you can never die. You have the ability to turn any thought into form with the power of your mind."
Wayne Dyer