Answer: The Creator created only one soul. It split into many parts, the so-called individual souls, each of which corrects itself only to facilitate common correction. But generally, the soul is one for all. Baal HaSulam writes about this in the article “600,000 Souls.”
Since all individual souls are in one aggregation of souls, the correction of one soul helps the other and so on.
From the Kabbalah Lesson in Russian 5/21/17