"Develop a lively devotion for Our Mother. She knows how to respond in a most sensitive way to the presents we give her. What is more, if you say the Holy Rosary every day, with a spirit of faith and love, Our Lady will make sure she leads you very far along her Son's path."
Saint Josemaria Escriva
The Rosary is made up of two things: mental prayer and vocal prayer. In the Holy Rosary mental prayer is none other than meditation of the chief mysteries of the life, death and glory of Jesus Christ and of His Blessed Mother. Vocal prayer consists of saying fifteen decades of the Hail Mary, each decade headed by an Our Father, while at the same time meditating on and contemplating the fifteen principal virtues which Jesus and Mary practiced in the fifteen mysteries of the Holy Rosary.
Since the Holy Rosary is composed, principally and in substance, of the Prayer of Christ and the Angelic Salutation, that is, the Our Father and the Hail Mary, it was without doubt the first prayer and the first devotion of the faithful and has been in use all through the centuries, from the time of the Apostles and disciples down to the present.
But it was only in the year 1214, however, that the Holy Mother Church received the Rosary in its present form and according to the method we use today. It was given to the Church by Saint Dominic who had received it from the Blessed Virgin as a powerful 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 unceasingly 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 Almighty 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 battering ram 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."
Ever since Saint Dominic established the devotion to the Holy Rosary up until the time when Blessed Alan de la Roche re-established it in 1460 it has always been called the Psalter of Jesus and Mary. This is because it has the same number of Angelic Salutations as there are psalms in the Book of Psalms of David. Since simple and uneducated people are not able to say the Psalms of David the Rosary is held to be just as fruitful for them as David's Psalter is for others.
But the Rosary can be considered to be even more valuable than the latter for three reasons. Firstly, because the Angelic Psalter bears a nobler fruit, that of the Word Incarnate, whereas David's Psalter only prophesied His coming. Secondly, just as the real thing is more important than its prefiguration and as the bodyis more than its shadow, in the same way the Psalter of Our Lady is greater than David's Psalter which did no more than prefigure it. Thirdly, because Our Lady's Psalter (or the Rosary made up of the Our Father and Hail Mary) is the direct work of the Most Blessed Trinity and was not made through a human instrument.
Our Lady's Psalter or Rosary is divided up into three parts of five decades each, for the following special reasons:
To honor the three Persons of the Most Blessed Trinity
To honor the life, death and glory of Jesus Christ
To imitate the Church Triumphant, to help members of the Church Militant and to lessen the pains of the Church Suffering
To imitate the three groups into which the Psalms are divided
the first being the purgative life
the second for the illuminative life
and the third for the unitive life
And, finally, to give us graces in abundance during our lifetime, peace at death, and glory in eternity.
Ever since Blessed Alan de la Roche re-established this devotion the voice of the people, which is the voice of God, called it the Rosary. The word Rosary means "Crown of Roses," that is to say that every time people say the Rosary devoutly they place a crown of one hundred and fifty-three white roses and sixteen red roses upon the heads of Jesus and Mary. Being heavenly flowers these roses will never fade or lose their exquisite beauty.
So the complete Rosary is a large crown of roses and the Rosary of five decades is a little wreath of flowers or a small crown of heavenly roses which we place on the heads of Jesus and Mary. The rose is the queen of flowers, and so the Rosary is the rose of all devotions and it is therefore the most important one.
[Source: The Secret of the Rosary by Saint Louis de Montfort]