The concept/reality of disease is strongly connected in the Torah to that of exile. The people (or individual) in exile has been banished from its source, from its homeland. Estrangement, whether on the spiritual or physical plane, is equivalent to disease. In general, disease–weakness–is the estrangement of the soul from the body; in the terminology of Kabbalah andChassidut, the estrangement of the light from the vessels (as in the primordial world of Chaos, a reality that experienced disassociation and distancing of its lights from its vessels and thereby broke, became sick, and ultimately died).
We find the juxtaposition of the two concepts of exile and sickness in the idiom "this sick exile" (as this idiom is read in Chassidut).
The Zohar goes so far as to say that the Shechinah (God's Divine Presence in creation, His infinite, immanent light that "fills all worlds") itself is "sick" in exile (the exile of the Jewish people). Rabbi Shneur Zalman of Liadi explains this at length in the Tanya.
The blood relates to the sefirah of binah, the mother-principle–"the mother gives her child the red [the blood]." The final and most extended exile, that exile referred to by the prophet as “the sick exile is the exile of Edom, from the word "red" (adom) and "blood" (dam).
In Chassidut it is explained that the consummate rectification of the mother principle in the soul is through unbounded love for one's fellow Jew. Here, one experiences the entire Jewish people together, in love and fellowship, under the protective wings of the Divine "mother." Loving all Jews as oneself connects all of the limbs of the Divine "body"; the love itself is the life-giving blood that unites all of the body's limbs. The word for "blood" (dam) is associated with the word for "man" (adam), which connotes in particular the Jewish people as a whole. Only by unbounded love (ahavat chinam) for all of Israel do we rectify the cause of "the sick exile," causeless hatred (sinat chinam).
Our sages teach that all exiles of the Jewish people, including the last–the exile of Edom–reflect (different aspects of) the first, archetypal exile–the exile of Egypt. In Kabbalah, Egypt also corresponds, in impurity, to the womb of the mother (the exodus from Egypt is the birth of the people of Israel from this impure womb). Thus, all exile, as all disease, begins and ends with the malfunctioning of the blood.
The malfunctioning of the blood results in the weakening of the immune system. In the terminology of Kabbalah: "binah extends until hod," as will be explained.
The Torah draws a further comparison to the state of exile (a spiritually diseased state) and its connection to the property of hod–an immune system property. We find that the angel of Esau injured Jacob's left thigh; this injury ultimately sent Jacob and his children into exile and signifies, in general, the nature of the exile of the Jewish people.
The left leg or thigh is identified with hod. This is the limb most vulnerable to injury. This relates as well to the body's system–the immune system–most susceptible to disorder, confusion, and inability to distinguish between Esau and Jacob. With Jacob’s victory over Esau’s angel, it was essential for him to re-establish and reinforce his very identity. He forced the angel to bless him with his true name, not known till then–Israel.
In conclusion, when we rectify our ability to acknowledge and thank God for everything that we have, to relate to Him above logic and reason, and return to Him in submission (all characteristic of the soul's rectified power of hod), we will then be healed from the illness of exile and will be able to experience our return to health and redemption. Thus, we find thathod is the vulnerability to disease (for that is where the angel attacked), as well as the point where disease is overcome–where we are weak is precisely where we can become strong; where we can get sick is where we can be healed. Thus, in every illness is embedded the clue to the nature of the cure itself.