Answer: The soul is one single whole, or in other words, the universal connection according to an altruistic tendency, according to the characteristic of bestowal. The worlds are found within the soul, and we discover them as levels of connection between us.
There are five worlds. In every world there are five Partzufim. And in every Partzuf there are five Sefirot—a total of 125 levels of approaching the Creator. All of the worlds gradually disappear with continuous approach, and only “we” remain, occupying the entire volume between us.
Question: What is the soul made of, what is its substance?
Answer: The soul consists of a desire for pleasure. This never changes because that substance always remains the same.
From the Kabbalah Lesson in Russian 10/30/16