Luke 2:35: And thy own soul a sword shall pierce, that, out of many hearts thoughts may be revealed.
Luke 2:51: And he went down with them and came to Nazareth and was subject to them. And his mother kept all these words in her heart.
Devotion to the Sacred Heart of Jesus focuses mostly on His divine love for mankind and encourages our humility, gratitude, obedience, and adoration; devotion to the Immaculate Heart of Mary focuses on Mary's love for God and encourages our emulating her humility, gratitude, obedience, and adoration. Mary as loving Mother of Jesus Who suffered for us; Mary as Mother of the Church; Mary as obedient daughter, Mary as our Gevirah (Queen Mother of Israel) -- we ponder her interior life in each of these roles, consecrate ourselves to Jesus through her, make reparations for offending her as our Mother, ask her intercession for us with her Son, and emulate her as the model of Christian perfection.
While, early on, of course, the Church Fathers wrote of Mary's blessedness, purity, and sorrows, and our Saints -- Dominic, Gertrude, Thomas Becket, Bridget, Bernardine of Siena, Louis de Montfort -- have always had deep Marian devotions, it was after the apparitions of Mary experienced by St. Catherine Labouré at Rue Du Bac, Paris in 1830 that devotions specifically to Mary's Immaculate Heart became formalized.
Mary appeared to St. Catherine Labouré standing on a globe, rays of light streaming from her fingers, enframed in an oval frame inscribed with the words, "O Mary, conceived without sin, pray for us who have recourse to thee." The whole vision "turned" showing the back of the oval inscribed with the letter "M" entwined with a Cross, and the hearts of Jesus and Mary, the former surrounded with thorns, the latter pierced with a sword. 12 stars circled this oval frame. Mary told her to strike a medal in this form -- a medal now known as the "Miraculous Medal" -- and that all who wore it properly after having it blessed would receive graces. The wearing of the Miraculous Medal has become one of the most common devotions to the Immaculate Heart.
Devotion to the Immaculate Heart became even more popularized after Mary's appearing to the three young shepherd children at Fatima, Portugal in 1917 (before the Russian Revolution), when she asked that Russia be consecrated to her Immaculate Heart to prevent the spread of "the errors of Russia." Eight years later, in 1925, Mary appeared to one of the visionaries -- Lucia, who'd since become a nun -- and requested reparations for the various ways in which her Immaculate Heart was offended -- such as attacks against her Immaculate Conception, virginity and divine maternity, and for those who teach their children contempt of Mary or who insult her by desecrating her images.
To make these reparations, she asked that we do 5 things, all with the intention of making reparation to her Immaculate Heart:
- recite at least Five Decades of the Rosary every day
- wear the Brown Scapular
- offer our daily duty to God as an act of sacrifice (ie., make the Morning Offering)
- make Five First Saturdays of Reparation to Her Immaculate Heart (see below)
- the Pope, in union with all the bishops of the world, must consecrate Russia to Her Immaculate Heart. Russia would be converted through this means, and a period of peace to be given to the world. If this is not done (and it hasn't been done), Russia will "spread her errors throughout the world." This consecration must be of Russia -- not "the world," but Russia by name.
- going to Confession (may be 8 days before the Saturday as long as one stays in a state of grace)
- receiving the Eucharist
- praying 5 decades of the Rosary, including the Fatima Prayer
- "keeping her company" for 15 minutes while meditating on all of the Mysteries of the Rosary with the intention of making reparation to her. This can be done by reading Scripture or other writings relevant to the Mysteries, meditating on pictures of the Mysteries, or simple meditation.