Originally published in Tzvi M. Rabinowicz (ed.), The encyclopedia of Hasidism (1996), pp. 3-4.
Son of R. Moses Horowitz, a descendant of R. Isaiah Horowitz, he was born in Orsha in the district of Moghilev. In his youth, Aaron became a disciple of R. Shneur Zalman of Liady, and he stated that he sat at R. Shneur Zalman’s feet for a period of thirty years. He is indeed generally considered to be the favorite and most distinguished pupil of the master.
For a considerable period, R. Aaron and R. Dov Baer (R. Shneur Zalman’s son) studied together as devoted friends and companions. When R. Shneur Zalman was arrested, R. Aaron collected vast sums of money to facilitate his liberation.
In the course of time, a serious quarrel appears to have broken out between R. Aaron and R. Dov Baer. Apart from the natural rivalry, which seemed to have developed between son and eventual successor of the master, and his favorite pupil, there is a good warrant for the opinion that the two men differed in their conception of the role of ecstasy in the mystical life. R. Dov Baer was exceedingly strict in his rejection of the slightest trace of sham emotion during Divine worship. Whereas R. Dov Baer is said to have recited his prayers in complete silence and immobility, the reports narrate that R. Aaron’s prayers were of a frightening intensity and were an outpouring of religious fervor and enthusiasm, with R. Aaron’s expressing himself in a mighty roar as his prayers were pronounced.
Aaron set up a rival hasidic court in Starosselje after the death of R. Shneur Zalman and R. Dov Baer’s succession to the leadership of the Habad group. From the year 1813 until after his death, R. Aaron’s followers were known as “Starosseljer hasidim.” At one time, R. Aaron was arrested, but he was released on 10 Kislev.
Aaron died some ten months after the death of R. Dov Baer. Some of his followers then changed their allegiance to Lubavitch; others accepted R. Aaron’s son, R. Hayyim Rafael, as their master in Starosselje. After a few years, when R. Hayyim Rafael died without leaving a successor in the Starosselje line, some of the diehards among the Starosselje hasidim preferred to remain without a master rather than to be led by a stranger, but the majority of them became followers of R. Menahem Mendel of Lubavitch.
He was the author of Bad Kodesh on Megillat Ruth (Warsaw, 1872); Sod Kedoshim, a commentary on the Passover Haggadah; Avodat HaLevi on the Pentateuch and festivals, printed in Lvov in 1842, and a second part, printed in Lvov in 1846; Shaar HaTefillah (Lvov, 1862); Shaar HaYihud VeHaEmunah (Gate of Unity and Faith), dealing woth the theme of Divine unity (Shklov, 1806).
Aaron planned his work to correspond to R. Shneur Zalman’s book, on which it is a commentary. Thus the first volume in an extended commentary on the second part of the Tanya, while the bulk of the second volume is a commentary on the first part of the Tanya. The fifth and final gate of Aaron’s second volume is a commentary on the third part of the Tanya.
L. Jacobs, Seeker of Unity.