Question: Baal HaSulam writes that in spirituality nothing is divided into parts. So, where does the concept of division into ten Sefirot come from?
Answer: The concept that spirituality is not divided into parts means that you cannot take a part from a given Partzuf (a spiritual system) and do whatever you want with it.
As soon as you take a part out of it, its structure immediately becomes complex and includes ten Sefirot. In other words, every grain of sand, or whatever it may be, is composed of ten Sefirot: this is true for both the whole and the part, every part of a part, and every part of the whole.
It is impossible to disconnect and separate the ten Sefirot; there cannot be less. If there seem to be more than ten, these ten Sefirot have been magnified. In any case, their number will be ten, no less and no more. In other words, they can be more qualitatively, but not quantitatively.
From the Kabbalah Lesson in Russian 3/5/17