The book of the great Kabbalist of the 16th century: Ari’s The Tree of Life, of course, is not easy and this is especially so for beginners. But Baal HaSulam wrote a commentary on it, which you can gradually understand and this is where people who come to Kabbalah start during the first few years of study.
TES begins with the words of Ari.
Know that before the emanated beings were emanated and the created beings created, an upper, simple light had filled the entire reality. There was no vacant place, such as empty air and space, but everything was filled with that simple, boundless light. It did not have a quality of Rosh, or Sof, but it was all one, simple light, completely even, called light of Ein Sof (Baal HaSulam, The Study of the Ten Sefirot).
This is about the fact that when there were no created beings as such, there was only one interesting substance called “the upper simple light that fills the entire reality.”
When reading these lines, questions immediately arise: What is a simple light? What kind of reality does it fill? What happened before it filled this reality? What does it represent? What does it mean that there was no free space, but the upper light was filling everything?
Moreover, Ari emphasizes that there was no free place in the form of empty air or empty space and everything was filled with infinite simple light. And, as he writes, there was neither beginning nor end in it, but everything was one simple, completely even light, which is called the light of infinity.
From KabTV’s “The Study of the Ten Sefirot” (TES), 8/14/22