The righteous man - the Tzaddik Reb Michele Zlotchover was a talented composer and one of the main singers of his Rebbe, the Ba'al Shem Tov.
Once Reb Michele was ill and could not bask in the presence if his Rebbe, he composed at that time the melody known as "Reb Michele Zlotchover's Melody of yearning."
The soft, exalted tones of the melody express the Chassd's longing for his Rebbe; the inner joy he experiences in the presence of his Rebbe; and his spiritual bind with and total devotion to his Rebbe.
Before his histalkus on the first day of Shavuos 5520 (1760), the Ba'al Shem Tov instructed his talmidim to sing the niggun composed by Reb Michel Zlotchover, known as the Hisorerus Rachamim Rabim Niggun (niggun that induces enormous mercy), and said: “I promise for all generations, that wherever, whenever and whoever will sing this niggun with a true awakening of teshuva, I will hear it in any heavenly heichal I may be and I will join in song to awaken much heavenly mercy for the baal teshuva singing the niggun.”
The Rebbes of Chabad would often sing this melody during prayer service and on auspicious occasions. It is considered a heavenly niggun, and is often used as a vehicle for stirring deep repentance.
In a talk in 1941, the Previous Rebbe described an episode that took place in 1916 on Pesach. Reb Michoel Devorkin sang this niggun for the Rebbe Rashab at a Farbrengen. At the conclusion of the niggun, the Rebbe Rashab said that he had heard two versions of this niggun. His father, the Rebbe Maharash, chose Reb Michoel Devorkin’s version. The Previous Rebbe later repeated his father’s comment on Reb Michoel Devorkin’s singing of the niggun, “In this niggun we sense the Ba'al Shem Tov.”
In Leningrad, the Previous Rebbe once handed Reb Michoel Devorkin a cup of mashke and requested that he sing the niggun. Reb Michoel Devorkin said, “Anytime the Rebbe will give me a cup of Mashke, I will sing the niggun of Reb Michela.”
In 1978, Reb Yaakov Katz of Chicago, who merited to exceptional kiruvim from the Previous Rebbe and the Rebbe, requested a Yechidus after Yud Shvat because he had something special to show the Rebbe. The Rebbe approved an appointment for Yechidus. During the Yechidus, Reb Yankel played a tape of Reb Michoel Devorkin singing Reb Michel Zlotshuver’s niggun as well as another niggun. Reb Yankel asked the Rebbe if he knew who was singing. The Rebbe responded, “Yes, it is Reb Michoel Devorkin.” Later, the Rebbe instructed that these niggunim should be included in one of the Lubavitch Nichoach records. It is titled Shnei Niggunim. It contains the two niggunim, Reb Michel Zlotshuver’s niggun and the other niggun, both sung by Reb Michoel Devorkin in the 1940’s.