No one can object that this devotion is novel or of no value. It is not new, since the Councils, the Fathers of the Church, and many authors both past and present, speak of consecration to our Lord or renewal of baptismal vows as something going back to ancient times and recommended to all the faithful. Nor is it valueless, since the chief source of moral disorders and the consequent eternal loss of Christians spring from the forgetfulness of this practice and indifference to it.
Some may object that this devotion makes us powerless to help the souls of our relatives, friends and benefactors, since it requires us to give our Lord, through Mary, the value of our good works, prayers, penances, and alms-giving."
Source: St. Louis de Montfort in Devotion to Mary