Praying the rosary daily—for me initially, the five decade form, but once I learned better, the traditional 15 decade rosary is now the rosary I pray daily—is the most powerful work that can be done to support the Church and an apostolate; something I firmly believe and something that has been part of suggested daily practice since the beginning of this apostolate.

St. Montfort says about the Rosary: “Almighty God has given it to you because He wants you to use it as a means to convert the most hardened sinners and the most obstinate heretics.” (p. 7) St. Louis Mary De Montfort (First published in the 18^th Century, English Translation 1954). The Secret of the Rosary. North River Press: New York.

There is no more effective weapon to use in the conversion of criminals than the Rosary, and if you are involved in an apostolate helping in the conversion of criminals it would behoove you to pray it daily, the full 15 decades, as St. Montfort wrote:.

FIRST ROSE: PRAYERS

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 if His Blessed Mother. Vocal prayer consists in saying fifteen decades of the Hail Mary, each decade headed by an Our Father, while at the same time meditation on and contemplating the fifteen principal virtues which Jesus and Mary practised in the fifteen mysteries of the Holy Rosary.

In the first five decades we must honor the five Joyous Mysteries and meditate on them; in the second five decades the Sorrowful Mysteries and in the third group of five, the Glorious Mysteries. So the Rosary is a blessed blending of mental and vocal prayer by which we honor and learn to imitate the mysteries and the virtues of the life, death, passion and glory of Jesus and Mary. (Ibid. p. 16)

And Fatima resulted in one addition, as the Catholic Tradition website (which also has The Secret of the Rosary complete online) notes:

Web Master’s Note:

St. Louis de Montfort wrote this classic work before Our Lady of Fatima came from Heaven. Tradition has set the form for the Rosary, and man ought not to change it. However, Our Lady may, since she gave it to St. Dominic, the Rosary is hers. When she came to Fatima she gave the three children and us through them, the Decade Prayer, to be recited:

DECADE PRAYER

(To be said after the Glory Be at the end of each decade of the Rosary)

O MY JESUS, forgive us our sins, save us from the fire of Hell,

lead all souls to Heaven, especially those who are most in need of Thy mercy.

(Retrieved February 25, 2019 from http://www.catholictradition.org/Classics/secret-rosary1.htm