The theological foundation of the Legion of Mary's lay apostolate. This work explains Mary's role in the church's missionary work and thoroughly examines the theology behind the Legionary Promise. This book explains that the lay apostolate is not merely an additional task, but a vocation for Catholics rooted in the Sacraments of Baptism and Confirmation. It places Mary as the perfect model for apostolic work. The presence of Our Lady in the Legion is not merely a devotion, but a mystical collaboration with the Holy Spirit to bring Christ to the world. It also explains how a legionary (member of the Legion) is called to surrender his or her entire being to Mary, so that Our Lady can work fully through their service to others.