The primordial light and darkness can be understood as a parable for good and evil. Clues: God creates light, and although in our physicality darkness is the absence of light, which we know to be made of distinct quanta, the “darkness” seems, according to the plain meaning of the text, to be an entity unto its own, and even once the light is created, the light and darkness are still mixed up to the extent that God has to “separate” the two, and He describes the light as “good.”
Throughout the rest of the Torah, darkness and light are metaphors for good and evil. The difference between the two is as stark and defined as the difference “between the holy and the profane, the Sabbath and week, and Israel and the nations.” However, in this world, we have the chance to morally obfuscate, to lose our moral compass, to mix the light and darkness. We are therefore bidden to recognize and sanctify these distinctions, and this is what Abraham stood for. Our sages used the imagery of the chaos that existed before the creation of the light to describe world history before the advent of Abraham, who endowed the world with moral clarity.