Kesher Gudal (“Thumb Joint,” a reference to Menachot 42a) discusses the laws of tefillin, tzitzit, and prayer, and is part of Avodat HaKodesh (“Work that is Holy”), a compilation of seven short works of law, custom, and ethics written in the late 18th century by Rabbi Chaim Yosef David Azoulai (known as the “Chida” for his acronym). Avodat HaKodesh incorporates talmudic, rabbinic, and kabbalistic teachings, translating them into practical instructions for a proper and holy life. The first Hebrew book to be printed in Jerusalem, it has since been published in more than a hundred editions.