If the third story of a house should collapse, it would become a two-story house.
But if one's head were removed, one would no longer be a man.
When we speak of an organic entity, such as Knesset Israel, we cannot distinguish between a thing apart and a thing that is flawed.
For what is partial is flawed–to the point that it cannot maintain its identity.
A parable may help us understand this idea.
Someone injured in a traffic accident was visited at the hospital by his relatives.
When they entered the room, they saw that he had lost his eyes.
Lifting the sheet,they saw that he had lost his hands, and lifting it still further, they saw that he had lost his feet.
But the doctor entered and reassured them, "You have nothing to worry about. His heart is fine!"
When one limb and then another is removed from the Jewish corpus, the mind and heart may still be functioning, but the totality has been grievously affected.
Some Jews correspond to the heart or mind–as long as they remain, then theoretically the Jewish people can continue to exist.
But should the Jewish entity be missing hands, feet, or eyes, the structure is no longer the same.
The problem of Jews missing from the whole is therefore not just demographic but qualitative.
There are hundreds of thousand of Jews across the world without whom the principal centers of Iewish life can continue to exist–but only like the man who lies in the hospital without eyes, hands, or feet.
If a limb is so diseased that it is liable to cause one's death, it must be amputated–however, the consequence will be far from trivial.
The Baal Shem Tov waged a fierce battle against the Frankists throughout his life.
Yet when they had converted to Catholicism, he grew deeply upset and exclaimed that "The Shekhinah cries out for their sake" (Shivkhei haBesht).
He explained that as long as a limb is connected to the body, even if it has shriveled, it may still recover.
But once the limb is severed, it is gone forever.
And every Jew is a limb of the Shekhinah.
This analogy has a more far-reaching implication as well: not only is the well-being of each limb dependent on the soundness of the others, but each is also intimately interrelated with every other.l
They are deeply intertwined, each existing within the other, appearing in it, influencing it, and being influenced by it.
For instance, a person's tooth bears an imprint of all the experiences that he has undergone-that he broke his hand at a certainage, the various diseases from which he has suffered, and so forth.
An impression of all of these is left on each tooth.
Similarly, whatever happens to any Jew (physically or spiritually) affects every other Jew wherever he may be, even if that effect is not consciously perceived.
–Rabbi Adin Steinsaltz
From Understanding the Tanya, Chapter 32, Rabbi Adin Steinsaltz