God wanted us to receive everything through Mary

That the Blessed Virgin Mary is the Mediatrix of all graces is not a new doctrine, and the Office and the Mass approved by Pope Pius XI are only the official confirmation of a truth which flows from the divine maternity of Mary and from the divine plan of salvation.

This feast derives from the whole doctrine of the Church and from the teaching of the Doctors and Saints. Among those are St. Ephrem, St. Bernard, St. Bernardine, and St. Louis de Montfort, whose Treatise on True Devotion to the Blessed Virgin is a magnificent illustration of this universal mediation of the Mother of God.

Mary's title par excellence, her supreme Glory, the principle of all her greatness and all her virtues, is her divine maternity.

If Church Tradition calls her the Treasurer of the Kingdom of Heaven, All-powerful Advocate, Dispenser of Grace, Co-redemptrix, Queen of Heaven and Earth, etc., it is because of her divine maternity.

But the title that seems to best sum up all the others and most adequately express the mission of the glorious Mother of God is that of Mediatrix of all graces, Mediatrix of intercession, and moreover, Mediatrix of the dispensation and distribution of all graces.

It is indeed to this doctrine that these words of the greatest Doctors and servants of Mary refer: everything that is applicable to God by nature is applicable to Mary by grace...

It was God's will that we should receive everything through Mary. All the gifts, virtues, and graces of the Holy Spirit himself are administered by the hands of Mary, to whomever she wishes, whenever she wishes, and as much as she wishes...

All the feasts and office of the Virgin Mary postulate or express the doctrine of Mary as universal Mediatrix of all graces.

Source: Abbé L. Jaud, Vie des Saints pour tous les jours de l'année, Tours, Mame, 1950.