Traditional mystical concepts permeate mainstream Jewish thought to this day (for example, the notions of tikkun ha-olam, or repair of the world, and of tzimtzum, God’s self-limiting), and texts of mystical origin have penetrated Jewish liturgy (including Lecha Dodi, the Friday night hymn welcoming the Sabbath, and other liturgical poetry). In addition, the academic study of Jewish mysticism has flourished in recent decades, due primarily to the work of a single scholar, Gershom Scholem. Scholem discovered and interpreted a wide range of mystical manuscripts and shed light on the origins and development of Jewish mysticism. With the emergence of New Age spirituality, Jewish mysticism has also experienced a popular renaissance. Jewish groups like the Renewal movement teach mysticism to spiritually inclined, nontraditional Jews, while controversial institutions such as the Kabbalah Centre offer a more universal and magical mysticism to Jews and non-Jews alike.