The Legion of Mary Handbook states that the "object of the Legion of Mary is the glory of God through the holiness of its members developed by prayer and active co-operation, under ecclesiastical guidance, in Mary's and the Church's work of crushing the head of the serpent and advancing the reign of Christ."  

"Holiness Developed by Prayer"

The spirituality of the Legion of Mary is founded on prayer - devotional prayer, particularly the Holy Rosary with zealous meditation on Holy Scriptures, Liturgy of the Hours, Novenas, Adoration of the Blessed Sacrament, and above all, frequent, if not, daily participation in the highest form of prayer, the Holy Sacrifice of the Mass. In the faith journey of the Legionary, is the gradual development of frequenting the sacrament of Penance or Confession and the worthy reception of the Holy Eucharist. The member of the Legion, though not a saint (yet), is expected to lead a prayerful and virtuous life as exemplified by the Blessed Mother. 

"Active cooperation with ecclesiastical guidance, in Mary's and the Church's work in crushing the head of the serpent..." 

The holiness of the Legionary does not end in prayer, but rather begins with it and continues in the active work of apostleship, i.e. the salvation of souls. Thus, the Legion cooperates with the priests and bishops in their work of crushing the head of the serpent, Satan. The Legionary is constantly engaged in this battle, as for the Legion, the soul is priceless. Every member commits to this work of salvation.  

"Advancing the Reign of Christ" 

The final end of all Legionary apostolic works is the victory of Christ. This victory could only be won through the salvation of souls.