Talmud Eser HaSefirot is the Ba’al HaSulam’s masterwork. It presents an orderly and systematic collection from among the writings of the Arizal, in sixteen volumes, with a relatively short commentary called Or Penimi and a broad, comprehensive commentary called Histaklut Penimit. At the end of every volume there is a question-and-answer section that provides a clear summary of its concepts and ideas. Talmud Eser HaSefirot was published between 1933 and 1937.