Answer: It is because the eight billion people who populate this planet are an integral system in itself that is made of ten Sefirot. Ten Sefirot is the system of humanity, a powerful system that has ten components, and is one whole and unique which includes all of us and all of our attributes.
Kabbalists study and explore the system: who is in it, which part he belongs to, how the nations connect within it, and how it can be led to total integral unity. Then, all of humanity will be balanced with nature that surrounds us, and we all will ascend to the next level of our evolution, to another dimension.
A person who studies the wisdom of Kabbalah and perceives it, sees these ten Sefirot. On the one hand, he is incorporated in them, in their action, and at the same time, he still is tied to humanity by his feet and must care about its ascent.
From the Kabbalah Lesson in Russian 11/8/15