Just as devotion to the Sacred Heart of Jesus is essential, for it highlights the redeeming love of the Incarnate Word, so also is devotion to the Immaculate Heart of Mary, since it emphasizes the co-redeeming love of the Mother of God.
Unlike the Heart of Jesus, the Heart of Mary does not participate in the hypostatic union and is, therefore, a purely human heart. It is the heart of the most perfect of creatures who took the love of God to the highest point possible and was closely united to the Heart of Jesus in a maternal and filial intimacy. This intimacy began with the Incarnation of the Word in her most pure womb, culminated with her final offering on Calvary—where She offered her Son for our salvation— and continues now in Heaven.
By the Heart of Mary, as Fr. José Maria Canal, CMF explains, “we understand her intimacy, maternal feelings, mercy and tenderness toward sinners.” For Pope Pius XII it is “a symbol of all interior life, whose moral perfection, merits and virtues are beyond all human understanding!”
Pius XII also emphasizes this maternal Heart’s compassion: “The Most Pure Heart of the Virgin [is the] seat of that love, compassion and all most lofty affections that participated so much in our redemption, especially when She ‘stabat iuxta Crucem,’ stood vigilantly next to the Cross.” (cf. John 19:25)