A person’s initial, simple, and undeveloped understanding of how God fills all worlds is that He is everywhere and fills everything, like the vacuum of space or, in a more concrete analogy, like the air that fills a room.
A deeper understanding of this concept is that “there is nothing besides Him,” that the multifaceted world that we perceive constitutes nothing other than God.
A material illustration of this idea is a black-and-white image.
It is not always clear which is the foreground and which is the background.
There are some images (such as those of the Dutch artist M. C. Escher) that are entirely focused on this liminal state.
The more a person looks, the more uncertain he grows as to which is the foreground and which is the background.
Rabbi Adin Steinsaltz