The Rosary is one of the greatest and most powerful devotions in the Catholic Church. It was in fact our Lady that gave the Rosary to St Dominic, who after three days of intense prayer and fasting had a vision in which our Lady gave him the Rosary describing it as “the weapon the Blessed Trinity wants to use to reform the world.” Revealed in three sets of mysteries: Joyful, Sorrowful, and Glorious, with 150 Hail Mary’s for the 150 Psalms, the Rosary was then preached by St Dominic to successfully convert the heretics of his day by explaining to them the mysteries of the faith.  In response, Pope Leo XIII observed, “Thanks to this new method of prayer… piety, faith, and union began to return; and the project and devices of the heretics to fall to pieces.” 
The Pontiff continued, “The efficacy and power of this devotion was also wondrously exhibited in the sixteenth century, when the vast forces of the Turks threatened to impose on nearly the whole of Europe the yoke of superstition and barbarism. At that time the Supreme Pontiff, St. Pius V., after rousing the sentiment of a common defence among all the Christian princes, strove, above all, with the greatest zeal, to obtain for Christendom the favor of the most powerful Mother of God. So noble an example offered to heaven and earth in those times rallied around him all the minds and hearts of the age. … Those who were unable to take part [as warriors in defense of the faith] formed a pious band of supplicants, who called on Mary, and unitedly saluted her again and again in the words of the Rosary, imploring her to grant the victory to their companions engaged in battle. Our Sovereign Lady did grant her aid; for in the naval battle…the Christian fleet gained a magnificent victory, with no great loss to itself….And it was to preserve the memory of this great boon thus granted, that the same Most Holy Pontiff desired that a feast in honor of Our Lady of Victories should celebrate the anniversary of so memorable a struggle, the feast which Gregory XIII. dedicated under the title of ‘The Holy Rosary.'”
This holy pope also described the effect of praying the Rosary: “with the spread of this devotion the meditations of the faithful have begun to be more inflamed, their prayers more fervent, and they have suddenly become different men; the darkness of heresy has been dissipated, and the light of Catholic faith has broken forth again.” 
The Blessed Mother appeared throughout recent centuries promoting the recitation of her Rosary. She appeared to St Bernadette at Lourdes in 1858 bearing a golden Rosary in her hand. In all 18 of those apparitions, Our Lady prayed the Rosary along with St Bernadette, saying the prayers other than those directed to herself.  Our Lady of Fatima, who appeared in 1917 to three shepherd children, was also holding a Rosary. She described herself as “the Lady of the Rosary” and urged all people to pray the Rosary daily for the conversion of sinners and to bring peace to the world.
On the necessity and benefits of praying the Rosary, Pope Leo XIII wrote over the course of fifteen years (1883-1898) twelve encyclicals and five apostolic letters. He famously wrote “The Rosary is the most excellent form of prayer and the most efficacious means of attaining eternal life. It is the remedy for all our evils, the root of all our blessings. There is no more excellent way of praying.”
“If you wish peace to reign in your homes, recite the family Rosary.” – Pope Saint Pius X
“The Rosary is a powerful weapon to put the demons to flight and to keep oneself from sin…If you desire peace in your hearts, in your homes, and in your country, assemble each evening to recite the Rosary. Let not even one day pass without saying it, no matter how burdened you may be with many cares and labors.” – Pope Pius XI
“There is no surer means of calling down God’s blessings upon the family than the daily recitation of the Rosary.” – Pope Pius XII
The Rosary is a timeless treasure through which the faithful receive great graces and grow closer to God through meditation on the mysteries. The Church has repeatedly recommended to all the faithful this most hallowed prayer through countless popes and Saints throughout the ages. A plenary indulgence has also been attached to “the recitation of the Marian Rosary in a church or public oratory or in a family group, a religious Community or pious Association”; a partial indulgence is granted in other circumstances. 
To become a saint, do what the saints do and follow their advice:
- St Francis de Sales said the greatest method of praying is: “Pray the Rosary”
- St Thomas Aquinas preached 40 straight days in Rome on just the Hail Mary.
- St. John Vianney could not be found without holding a rosary in his hand.
- Padre Pio prayed the 15 decade rosary as many as 35 times in a day and said, “The Rosary is The Weapon.”
- “The rosary is the scourge of the devil.” – Pope Adrian VI
- St Louis de Montfort described the Rosary as “the most excellent of all prayers.”
- “The rosary is the most powerful weapon to touch the Heart of Jesus, Our Redeemer, who so loves His Mother. – St Louis de Montfort
- “Never will anyone who says his Rosary every day be led astray. This is a statement that I would gladly sign with my blood.” ~Saint Louis de Montfort
- “When the Holy Rosary is said well, it gives Jesus and Mary more glory and is more meritorious than any other prayer.” – Saint Louis de Montfort
- “The holy Rosary is a powerful weapon. Use it with confidence and you’ll be amazed at the results.” ~St. Josemaria Escriva
The Fifteen Promises of Mary Granted to those who Recite the Rosary
The Blessed Virgin Mary promised to Saint Dominic and to all who follow that “Whatever you ask in the Rosary will be granted.” She left for all Christians Fifteen Promises to those who recite the Holy Rosary.
Imparted to Saint Dominic and Blessed Alan:
- Whoever shall faithfully serve me by the recitation of the Rosary, shall receive signal graces.
Signal Graces are those special and unique Graces to help sanctify us in our state in life. See the remaining promises for an explanation for which these will consist. St. Louis de Montfort states emphatically that the best and fastest way to union with Our Lord is via Our Lady [True Devotion to Mary, chapter four].
- I promise my special protection and the greatest graces to all those who shall recite the Rosary.
Our Lady is our advocate and the channel of all God’s Grace to us. Our Lady is simply highlighting that she will watch especially over us who pray the Rosary. [True Devotion to Mary, chapter four].
- The Rosary shall be a powerful armor against hell, it will destroy vice, decrease sin, and defeat heresies.
This promise, along with the next, is simply the reminder on how fervent prayer will help us all grow in holiness by avoiding sin, especially a prayer with the excellence of the Rosary. An increase in holiness necessarily requires a reduction in sin, vice, and doctrinal errors (heresies). If only the Modernists could be convinced to pray the Rosary! St. Louis de Montfort states “Since Mary alone crushed all heresies, as we are told by the Church under the guidance of the Holy Spirit (Office of the Blessed Virgin Mary)…” [True Devotion to Mary #167]
- The Rosary will cause virtue and good works to flourish; it will obtain for souls the abundant mercy of God; it will withdraw the hearts of men from the love of the world and its vanities, and will lift them to the desire for eternal things. Oh, that souls would sanctify themselves by this means.
This promise, along with the previous, is the positive part, that being to live in virtue. Becoming holy is not only avoiding sin, but also growing in virtue.
- The soul which recommends itself to me by the recitation of the Rosary, shall not perish.
Since Our Lady is our Mother and advocate, she always assists those who call on her by praying the Rosary. The Church reminds us of this in the Memorare prayer, “never was it known that anyone who fled to your protection, implored your help or sought your intercession, was left unaided”
- Whoever shall recite the Rosary devoutly, applying himself to the consideration of its sacred mysteries shall never be conquered by misfortune. God will not chastise him in His justice, he shall not perish by an unprovided death; if he be just, he shall remain in the grace of God and become worthy of eternal life.
This promise highlights the magnitude of Graces that the Rosary brings to whomever prays it. One will draw down God’s Mercy rather than His Justice and will have a final chance to repent (see promise #7). One will not be conquered by misfortune means that Our Lady will obtain for the person sufficient Graces to handle said misfortune (i.e. carry the crosses allowed by God) without falling into despair. As Sacred Scripture tells us, “For my yoke is sweet and my burden light.” (Matthew 11:30)
- Whoever shall have a true devotion for the Rosary shall not die without the sacraments of the Church.
This promise highlights the benefits of obtaining the most possible Graces at the hour of death via the Sacraments of Confession, Eucharist, and Extreme Unction (Anointing of the Sick). Being properly disposed while receiving these Sacraments near death ensures one’s salvation (although perhaps with a detour through Purgatory) since a final repentance is possible.
- Those who are faithful to recite the Rosary shall have during their life and at their death the light of God and the plenititude of His graces; at the moment of death they shall participate in the merits of the saints in paradise.
Our Lady highlights the great quantity of Graces obtain through praying the Rosary, which assist us during life and at the moment of death. The merits of the Saints are the gift of God’s rewards to those persons who responded to His Grace that they obtained during life, and so Our Lady indicates that she will provide a share of that to us at death. With this promise and #7 above, Our Lady is providing the means for the person to have a very holy death.
- I shall deliver from Purgatory those who have been devoted to the Rosary.
Should one require Purgatorial cleansing after death, Our Lady will make a special effort to obtain our release from Purgatory through Her intercession as advocate.
- The faithful children of the Rosary shall merit a high degree of glory in Heaven.
This promise is a logical consequence of promises #3 and #4 since anyone who truly lives a holier life on earth will obtain a higher place in Heaven. The closer one is to God while living on earth, the close that person is to Him also in Heaven.
- You shall obtain all you ask of me by the recitation of the Rosary.
This promise emphasizes Our Lady’s role as our advocate and Mediatrix of all Graces. Of course, all requests are subject to God’s Most Perfect Will. God will always grant our request if it is beneficial for our soul, and Our Lady will only intercede for us when our request is good for our salvation.
- All those who propagate the Holy Rosary shall be aided by me in their necessities.
If one promotes the praying of the Rosary, Our Lady emphasizes Her Maternal care for us by obtaining many Graces (i.e. spiritual necessities) and also material necessities (neither excess nor luxury), all subject to the Will of God of course.
- I have obtained from my Divine Son that all the advocates of the Rosary shall have for intercessors the entire celestial court during their life and at the hour of death.
Since Our Lady is our advocate, she brings us additional assistance during our life and at our death from all the saints in Heaven (the Communion of Saints).
- All who recite the Rosary are my sons and daughters, and brothers and sisters of my only Son Jesus Christ.
Since the Rosary is a most excellent prayer focused on Jesus and His Life and activities in salvation history, it brings us closer to Our Lord and Our Lady.
- Devotion of my Rosary is a great sign of predestination.
Predestination in this context means that, by the sign which is present to a person from the action of devoutly praying the Rosary, God has pre-ordained your salvation. Absolute certainty of salvation can only be truly known if God reveals it to a person because, although we are given sufficient Grace during life, our salvation depends upon our response to said Grace. (See Summa Theologica, Question 23 for a detailed theological explanation). Said another way, if God has guaranteed a person’s salvation but has not revealed it to Him, God would want that person to pray the Rosary because of all the benefits and Graces obtained. Therefore the person gets a hint by devotion to the Rosary. This is not to say that praying the Rosary guarantees salvation – by no means. In looking at promises #3 and #4 above, praying the Rosary helps one to live a holy life, which is itself a great sign that a soul is on the road to salvation. (See also paragraphs 381, 488, 600, 2782 in the Catechism of the Catholic Church.) In fact, St. Louis de Montfort says even more strongly that “an infallible and unmistakable sign by which we can distinguish a heretic, a man of false doctrine, an enemy of God, from one of God’s true friends is that the hardened sinner and heretic show nothing but contempt and indifference to Our Lady…” [True Devotion to Mary, #30]
Reminder: these promises mean that, by faithfully and devoutly praying the Rosary, Our Lady will obtain for us the necessary Graces to obtain said promises. It is still up to each individual soul to respond to those Graces in order to obtain salvation.
Dr Taylor Marshall, How Mary Gave the Rosary to St Dominic.
 Pope Leo XIII, Apostolatus Officio: On Devotion of the Rosary, 1883.
 Fr Carota, Our Lady of Lourdes Apparition to St. Bernadette and The Holy Rosary.
 The Enchiridion Of Indulgences, Issued by the Sacred Apostolic Penitentiary, 1968.