Light

And God said, "Let there be light," and there was light. And God saw that the light was good. And God separated the light from the darkness. God called the light Day, and the darkness, he called Night. And there was evening and there was morning, the first day. - Genesis 1:3-5

Light, scientifically, is composed of material particles called photons.

Spiritually, it is the purest expression of higher meaning and was God’s first spoken word. Each component of the universe is a union of heaven and earth, each with a spiritual and material dimension. Dimensions are symbolized by a series of layers in vertical space, with top layers light, supple, simple, bright, and clear and bottom layers heavy, solid, complex, dark, and obscure. The top levels are more implicit and has less corporeal real presence.

Things that are too high are too simple to understand, while things that are too low are too complex. True knowledge is complex enough to be tangible while simple enough to be meaningful.

To the ancients, they played a role in the process of knowledge. Light is linked with spiritual reality, while dark is linked with corporeal reality. Corporeal reality asks a question with the power to host spiritual meaning when answered, so dark matters are considered a cause of revelation and manifestation. When ideas are too abstract to understand, we require detailed examples to appreciate its ramifications.

(The Language of Creation: Cosmic Symbolism in Genesis - A Commentary by Matthieu Pageau, 2018. Pages 35-40)