Your first and third answerers have fairly given the meaning.
Esoterically, the fifth essence follows the highest or quickest earthly element, fire/light (fire in this schema is focused light).
The lesser etheric is the fiery/light or fourth essence. What transcends the earthly octave are those aspects of the lesser etheric which pattern the Divine. In this way the soul, or soulfield energies, are saved, preserved. The "fiery trials" and "Our God is a consuming fire" are examples of this wisdom (wise dominion).
Some authors who deal with quintessence:
Mark Prophet, "The Path of the Higher Self,"
O. M. Aivanhov, "Light Is a Living Spirit" and Man's Two Natures: Human and Divine,"
Ann Ree Colton, "Watch Your Dreams" and "Kundalini West,"
Dr. Olga Kharitidi, "Entering the Circle" and "The Master of Lucid Dreams," and
Free and Wilcock, "The Reincarnation of Edgar Cayce?"