Rabbi Saadyah wrote the first Jewish work of philosophy in 933. Rabbi Bachaya wrote the first work of Jewish ethics more than a century later. Rabbi Saadya flourished during the twilight of once glorious Babylonian Jewry; Sephardic Jewry continued its magnificent history in Spain, reflecting the shift from Asia to Europe, where R. Bachaya lived and created his magnum opus, Duties of the Heart (Chovot HaLevovot).
Rabbi Bachaya lived in Muslim Spain, probably in Saragossa, and served as a judge, but little else is known about his life. He was thoroughly conversant with the entire Biblical and Talmudical literature and was also master of all the knowledge and science of his day.
Though a philosopher in his own right, Rabbi Bachayas essential contribution is that of creator of a new genre in Jewish literature, Jewish ethics. The first chapter of his work which is devoted to the unity of G-d employs philosophical arguments which some felt were not readily understandable and was skipped over by many students.
Rabbi Bachayas work, as indicated by its title, focused on the non-physical obligations of the Jew: the obligations of feeling, heart and mind in contrast to those mitzvot that involve the limbs. Pointing to the neglect of this group of mitzvot, he underscored their critical importance.
Rabbi Bachayas central focus was on Service of G-d and abiding by His will, and fulfilling the duties of the heart was viewed as the entree to nearness to G-d, the ultimate objective. Understandably, the tenth and last chapter of the book is Love of G-d.
Though emphasizing the importance of rational thought, Rabbi Bachayas real goal was the experience of G-d. A systematic, carefully constructed work, Duties of the Heart, has remained to this day a favorite of serious, sensitive students.
The Chatam Sofer studied with his students from Duties of the Heart for 15 minutes before his lecture in order to inspire their hearts with fear of G-d.. and almost all his musar was taken from that book (Chut HaMeshulash). And, Rabbi Yonah Landsofer, an eighteenth century gaon wrote, a person must attach himself to the Duties of the Heart from whence he can acquire the choice midot for the service of the Lord. And one must plummet it
Sources: Orthodox Union