In his youth, he studied Talmud and halachic texts. Under the influence of his maternal uncle, Rabbi Manly of Karlin, he became close to Rabbi Dov Ber, the "
Maggid of Mezeritch," who was the successor of the
Baal Shem Tov, and became one of his prominent disciples. He played a crucial part in the dissemination of Hasidism in Eastern Europe. He was a charismatic figure who brought the new teachings of Hasidism to
Pinsk, an area known as a stronghold of opposition to Hasidism. The Hasidic center he established in
Karlin (a suburb of Pinsk) acted in parallel to the center in Mezritsch. Together with Rabbi
Menahem Mendel of Vitebsk, he spread the teachings of
Hasidism throughout
Lithuania. The center in Karlin was so influential that its name became a general designation for the movement; by the last quarter of the 18th century, "Karliner" was a common name for all Hasidim among both European Jews and Russian authorities.
Solomon Maimon, in his
Lebensgeschichte published around 1792–1793, referred to Mezeritch and Karlin as the central locations of the new movement, noting that pilgrims traveled to Karlin and other holy places to hear the new doctrine. Aharon's authority in the community derived in part from his status as a disciple of the Maggid. He was involved in communal affairs, using his credentials as a disciple of the Admor (the Maggid) to reinforce the validity of new regulations, such as the
kropki tax legislation of 1769 in
Nieswiez, Lithuania, which aimed to protect the rights of the weaker members of the community. Some scholars attribute the emphasis on the social improvement of the lower classes, marking a social turn in Hasidism, partly to his activity in this regard. ==Teachings and Ethos==