The Mirror of Perfection (To Wit: The Blessed Francis of Assisi), written by Brother Leo, is a crucial early biography of St. Francis, focusing on his radical embrace of poverty, humility, and love for all creation, chronicling his life from worldly youth to spiritual leader, and preserving the original Franciscan ideals against later laxity, detailing his miracles, deep prayer, love for nature (like the Canticle of Brother Sun), and compassionate suffering for Christ's Passion. It serves as a testament to maintaining spiritual purity within the Franciscan Order.