Every apostolate depends absolutely on grace: to snatch souls from Satan can only be done by grace; to make a soul live the life of Jesus Christ absolutely requires the help of grace.
The man who evangelizes and the man who is evangelized both need the help of grace: for the first, an infinite series of graces is needed to prepare him for his apostolic mission; the graces of enlightenment, the graces to obtain conversions, the graces of perseverance. For the soul who is to be evangelized, there must be a grace to receive the apostle, then the graces of light, strength, docility etc.
But it is Mary who obtains all these graces. Without Her help, no sinner could pass from spiritual death to divine life; no upright person could ascend one degree towards holiness; no missionary, in spite of his eloquence, knowledge and skill, could succeed in converting a single soul.
Every true apostolate is the work of grace. Every grace presupposes an intervention by Mary. From the day of Her Assumption, all the souls who have been converted or sanctified, or will be converted or sanctified until the end of the world by the twelve apostles and their collaborators, by the countless multitude of priests and religious men and women - all those multitudes that no one can count, who will save themselves - all of them without exception owe their glory and their beatitude to the Mediatrix of all graces.
Mary is our mother. Every mother is the first apostle of her child: it is her mission to preserve the little being from sin and to make him or her live the supernatural life. If she entrusts it to other educators, they are only helpers: she remains the first person responsible for this mission.
All the more reason why Mary is the first apostle of her children, because she is their supernatural Mother; her motherhood consists entirely in giving supernatural life. What does she, in fact, do as a Mother? She calls us to the life of Jesus, she gives birth to us to this life; she preserves it, she maintains it, she makes us grow in it to perfection.
The apostles, the missionaries, and apostolic souls are only aids that Mary uses as instruments in Her Immaculate Hands so that in them and through them She acts as co-redemptrix and distributor of all graces: “Recourse to Mary's mercy requires each of the faithful to examine anew, with a resolution worthy of the great movements of human history, what contribution they can make to God's saving work in order to help a world which is heading, as it is today, towards its ruin” (Pope Pius XII, address of February 10, 1952).