Although it may be physically impossible to heal a mortally ill body, even by the Divine light of the Torah, nevertheless, it is possible for one's own soul to "take over" and "replace" the body by enacting all of its physical functions in its stead. The body remains mortally ill, as before (to the extent that by Torah law the person is defined as treif–about to die), but somehow he continues to live.
This is healing from the fifth level of the soul, the yechidah, "the single one." Of this level it is said, "as though the Holy One dwells in his guts." "The Holy One in one's guts" makes the body appear to be functioning normally although it is virtually dead. The truly transcendent sanctity of the Holy One is existentially separate and removed from the physical body; thus, the body is in no way affected or changed by the presence of the Holy One dwelling within it and "living" for it.
The yechidah–"the single one"–implies essential "singularity," as reflected by its ability to function independently (alone) in another (the body).
Of this level it is said, "the tzadik lives in his faith." In Chassidut, this is the level referred to as "essential life" (chai be-etzem), in contrast to "bestowing life" (chaim lehachayot), the life force of the chayah. Rather than bestowing life to the body (when this is physically possible), the yechidah "lives," in its essential state of life, for the body. This is by the power of the simple faith of the tzadik.
The sixth level of healing is the one for which we reserve the word "miracle" in its truest sense. Though all of the above levels of healing (from the second on) appear to be supernatural, it is at this level that the mortally ill body itself undergoes a miraculous, existential metamorphosis; the physical body becomes reborn.
Our sages teach us that at the time of the resurrection of the dead, bodies will come to life from the grave in exactly the same state of being and physical condition as they were upon the moment of death. Then, instantaneously, they will be healed.
The state of the first moment of resurrection–alive though ill as at the moment of death–corresponds to the fifth level of yechidah described above. The state of the second moment of resurrection–the rebirth of the body itself–corresponds to the sixth level, the revelation of the essence of the soul (the "spark of God" enclothed within the yechidah, as will be explained).
At this level, all manifestations of soul (i.e., the five previous levels from nefesh to yechidah) and body are one. The essential life of the soul and the eternal life of the body are the same.
An example of this sixth level of healing is the miracle of Chananiah, Mishael, and Azaria, as related in the book of Daniel. When thrown into the furnace by the order of the Babylonian king, the fire did not burn their bodies (although it did burn those of others around). The state of the body in fire is a physical analog to that of mortal, terminal disease. For the body to survive and emerge unaffected exemplifies the existential power of spontaneous rebirth.
This is the revelation of the Divine "holy of holies" of the soul, above the level of "as though the Holy One dwells in his guts," described above with regard to the yechidah. The Divine "holy of holies" imbues the soul of the would-be martyr (the consciousness of Chananiah, Mishael, and Azariah) with the power to metamorphose his physical body.
This level corresponds to the actual "spark of God" within the yechidah of the Jewish soul. This spark derives from the essence of the infinite light above, preceding the primordial contraction (tzimtzum). Subsequent to the tzimtzum, the possibility of an absolute miracle such as that described above is excluded from the perspective of creation. Nonetheless, the "spark of God" enclothed within each Jewish soul allows for the manifestation of such a miracle. This manifestation is the ultimate secret and purpose of the presence of the Jewish soul in creation.