Sartre was wrong
No, existence does not precede essence, tho it is easy to infer that from our human freedom to create and recreate ourselves.. I was sufficiently infatuated with Existentialism (and Phenomenology) to apply to grad school at Northwestern, which in 1963 was easily the best (and one of the few) programs featuring it prominently in the curriculum. The U. of Chicago had only one course, and that taught by an adjunct, Eugene Gendlin, who was mainly interested in phenomenological psychology, and later wrote a book on "Presence."
I loved Camus in particular at Grinnell, admiring his ability to alternate novels with absorbing philosophical essays. That love passed, but the intrigue of phenomenology stayed with me throughout my career. I was especially taken with Husserl, and then in my dissertation and beyond, his successor Alfred Schutz. (I never really connected with Heidegger, who once proclaimed: "Nothing nothings nothing.")
The idea of experiencing the Real without the benefit (and limitation) of intermediate sensory information still fascinates me.. the VOID, QED. indeed, this theme has led me to contemplate the manifestation point, the point at which spirit materializes, where energy becomes matter. For Pythagoras, Number (the Monad) is the most fundamental "element" of the Real: from it come Form and Measurement.. and Substance, the so-called Platonic solids. (insert long quote).
Metatron's Cube contains all the Platonic solids, and so represents unity and power. The Pythagoreans recognized the Divine Harmony of the Spheres, celestial geometry, as patterns of Reality, as Source, what Plato later called Form or Idea.
"Essence" is misleading, as is "Substance", although the idea of distillates and residues seems relevant to the matter-energy Idea. Imagine something like this: The pulsing "strings" (see earlier post) drip ovoid energy packets of information, which move as/where needed and change their vibration in the creation and sustenance of the material world. The "strings" are distinct but have no space between them; they are substance without mass, the thickening, vibrant spark in your DNA.
Sartre's hubris was the same as Ayn Rand's, diametrically opposed politically though they were: They shared a romantic attachment to the "individual" and a heroic distortion of the range and bounds of human free will. Humility in the recognition of appropriate human limits, and gratitude for the gift of life are more helpful attitudes than feeding the greedy human ego.