Rabbi Isaiah ben Avraham Ha-Levi Horowitz, known as the Shlah after the title of one of his major works Shnei Luchos Ha-Bris, was a renowned halachist, kabbalist and communal leader.
Born in Prague he moved with his father to Poland in his youth, and after building a reputation as an exceptional scholar, he gained a number of positions as head of beis dins (religious courts) in the area. By 1606 he reached the level of the head of the Frankfort on the Main beis din, one of the most influential of the period.
After the Jews were expelled from there in 1614, he returned to his native Prague, where he remained as a rabbi. In 1621 at the death of his wife, he moved to Eretz Israel, remarried and settled in Jerusalem as one of the heads of the Ashkenazic community there. In 1625 he was captured by the Arab ruler, and ransomed for an exorbitant sum. The Shlah died in Tiberius and is buried near the Rambam. During his life the Shlah was a wealthy and active philanthropist, supporting Torah learning especially in Jerusalem. In his many Kabbalistic, homiletic and halachic works, he stressed the joy in every action, and how one should convert the evil inclination into good, two concepts that impacted on Jewish thought through to the eighteenth-century, and greatly influenced the development of the Chassidic movement.