Essence-Function is how reality operates. It has its base in the Awakening of Faith in Mahayana, or Awakening of Faith in the Great Way, if you prefer. The unhindered interpenetration of all dharmas is reality. There is no seam between Absolute & elative Truths, there is no "and" or "but," and there is barely even a hyphen between Essence and Function. EssenceFunction is more accurate as a reflection of reality.
Think of "Essence" not as a soul or spirit, or a thing at all. It's the basis, it's ground zero, its behind everything, it's in the middle and front of everything. It's the noun. "Function" is how Essence is manifested, just as the Absolute only manifests through the relative and vice versa. There can be no Essence without Function, there can be no Function without Essence. Function is the verb.
If you look at the tangle of holiday lights you may have wrestled with recently, the lights are Essence, the untangling, hanging, and turning them on is Function. They are inseparable; there's no dividing line between them. In the end, the lights just do what lights do--throughout that whole process.
When we look at Buddha Nature as our Essence--the commonality among all of us--what is our correct Function? Is it to hate, slander, vilify, and malign ourselves and each other? Drop a dime in the Salvation Army bucket, donate something, or time, or money to someone less fortunate than you, and without any expectation of congratulations, no Great Cosmic "Attaboy."
Just be generous, compassionate, loving, and imperturbable in the face of difficulties, meeting your duties head on. Function is Peace on earth, good will to all sentient beings, peace on earth and good will to you.
Myeong Jin Eunsahn gave the Dharma talk on December 20, 2023.