The Jewish people as a unit comprises 600,000 souls (each one correlating to one of the 600,000 parts composing the totality of the world).
One may question this assertion based on the plain facts pointing to a greater number of Jews throughout the ages.
Addressing this question, the author of the Tanya explains that this number represents not the total number of Jewish souls, but rather the number of root souls, each of which is splintered into an additional 600,000 derivative souls.
The overwhelming majority of Jews in any given time or place do not possess a root soul, but rather a fragment, a spark of it.
The subdivision of fundamental root souls accounts for why people who to all appearances share nothing in common – being worlds apart in their opinions, lacking any familial connections or shared educational backgrounds – nevertheless feel a sense of kinship to one another.
There is an undetectable, quintessential soul force engendering often inexplicable feelings of closeness among people.
Their mutual sense of companionship and compatibility is on account of their kindred souls, each of which is a fragment of the same root soul.
Such people are not exactly the same because the soul fragments themselves are not necessarily of equal status.
For example, a particular soul offshoot may possess a unique intellectual bent, while its counterpart does not.
Despite such differences, these individuals will feel an inexplicable kinship with each other, like two shards of the same root soul.
The collective, root soul is analogous to the defining character of an overarching entity, while its “sparks” are components of that same character.
Just as the collective essence of the Jewish people is divided into 600,000 root elements, so each root soul is subdivided into 600,000 sparks.
These sparks, reflecting various facets and presenting unique perspectives of the root soul from which it originated, are gifted and bound to every one of us, providing the contexts for our unique paths of divine service in this world.
Rabbi Adin Steinsaltz