When the Sefer Yetzirah summarizes the essence of the sefirot, it does so by describing them as “of nothingness.” More so than any of the channels, they are united in a common being, which is no being, or a being so full that it exceeds being as a specific beings like planets and stars and animals. This nothingness divides itself and in dividing itself sets the tree in motion.
A long time ago now, I was discussing an article by Toshihiko Izutsu with a group of friends. I can’t recall the specific article at this remove (it was one found in Creation and the Timeless Order of Things), but it was one of his discussions of mystical experiences in Sufi literature. Over the course of the article, he made the comparison between descriptions of musical experience and descriptions of mystical experiences, highlighting how they are both resistant to direct description.