Below is an excerpt from the book The Light That Unites: A Chanukah Companion (OU Press) by Aaron Goldscheider.

There are several ways that one may fulfill the mitzvah of lighting the Hanukkah menorah. While one may certainly use wax candles, beeswax candles, paraffin, and an assortment of oils, the preferred way of lighting the menorah is with olive oil.

Why olive oil? Importantly, this is the oil that the Jewish people used to light the Menorah in the Holy Temple, and it was with olive oil that the miracle occurred. Today, when we light our menorahs using olive oil, we closely mirror the way the kohanim lit the Menorah in Jerusalem.

Yet, there are other reasons why olive oil is significant and contains special symbolism, especially on Hanukkah. For the Greeks, everything that was externally beautiful was good; to the Jew, everything that is inwardly good is beautiful.

The victory of Hanukkah was the victory of an inner essence over external appearance, of light over darkness. The olive is an appropriate symbol of this victory, for the light of the menorah comes from the oil of the olive. Although the olive seems to be just a small and undistinguished fruit, its outer appearance is misleading. There is actually so much more to the olive than meets the eye.

Inside this tiny fruit is the oil that can light an entire room. While the olive appears to be just a small and simple food, when transformed into oil, this simple fruit turns out to have contained light. Seeing the light that emanates from the olive’s oil, we are awakened to the possibilities of light hidden in other places, light packed into the simplest of physical things — waiting to be revealed through our usage and understanding. We are also reminded that if we look beyond the superficialities of this world, beyond the mask of darkness, we can perceive light.

At Hanukkah time the olives on the trees are late in their season and have been darkening from green to black. It is the black olives that contain the most oil. The blacker the olive, the more light it contains. Sometimes we need to wait, to bide our time, in order to have greater understanding.

The lighting of the menorah by the Maccabees was the victory of this patient understanding that there is so much more to the world than meets the eye. Hassidic tradition teaches that the word hashemen (הָשֶֽׁמֶן), “the oil,” has the same letters as neshamah (נשָׁמָה), “soul.” The oil is the hidden essence of the olive; the soul is the hidden essence of man.