Mary to Saint Dominic: “If you want to win souls over to God, preach my Rosary!”

It was in the year 1214 that the Church received the Rosary in its present form and 

according to the method we use today. It was given to the Church by St. Dominic, who had received it from the Blessed Virgin as a means of converting the Albigensians and other sinners. 

Saint Dominic, seeing that the gravity of people's sins was hindering the conversion of the Albigensians, withdrew into a forest near Toulouse, where he prayed continuously for three days and three nights. During this time he did nothing but weep and do harsh penances in order to appease the anger of God. He used his discipline so much that his body was lacerated, and finally he fell into a coma. 

At this point our Lady appeared to him, accompanied by three angels, and she said, "Dear Dominic, do you know which weapon the Blessed Trinity wants to use to reform the world?" 

"Oh, my Lady," answered Saint Dominic, "you know far better than I do, because next to your Son Jesus Christ you have always been the chief instrument of our salvation." 

Then our Lady replied, "I want you to know that, in this kind of warfare, the principal weapon has always been the Angelic Psalter, which is the foundation-stone of the New Testament. Therefore, if you want to reach these hardened souls and win them over to God, preach my Psalter."  (Second Rose)

The saintly Blanche of Castille, Queen of France, was deeply grieved because twelve years after her marriage she was still childless. When St. Dominic went to see her, he advised her to say the Rosary every day to ask God for the grace of motherhood, and she faithfully carried out his advice. In the year 1213 she gave birth to her eldest child, who was called Philip. But when the child died in infancy, the Queen sought our 

Lady's help more than ever, and had a large number of rosaries given out to all members of the court and to people in several towns in the Kingdom, asking them to pray to God for a blessing which this time would be complete. This was granted to her, for in 1215 St. Louis was born, the prince who was to become the glory of France and the model of Christian kings.  (Thirty-First Rose)

Saint Louis de Montfort, The Secret of the Rosary