He was chief rabbi of Hesse-Darmstadt and head of the Talmudical school at Frankfurt, which had been founded and richly endowed by his father-in-law, Samson Wertheimer, of Vienna.
For over half a century this school flourished under Kann's guidance, and maintained the high reputation of Frankfurt as a seat of Talmudic study.
By his energy and activity in behalf of the Jews, Moses Kann's name became celebrated throughout German Jewry.
By the testimony of the Berlin court preacher Jablonski and the consistorial councillor Scharden of Halle, supported by the opinion of twenty-four Christian professors and preachers who, in 1728, had declared that "neither the Jewish prayer-book nor the Talmud contained anything derogatory to Christianity," Moses Kann proved before the Elector of Mainz the bad character of the apostate.
Moses Kann's name is perpetuated in the memoir-book of the Frankfurt congregation; Meïr ben Eliakim Götz, in "Eben ha-Shoham," responsa, praises him as his benefactor, and Eleazar Kallir, in his preface to "Or Hadash," mentions him in terms of admiration.