1. it gradually gives us a perfect knowledge of Jesus Christ;
2. it purifies our souls, washing away sin;
3. it gives us victory over all our enemies;
4. it makes it easy for us to practise virtue;
5. it sets us on fire with love of Our Blessed Lord;
6. it enriches us with graces and merits;
7. it supplies us with what is needed to pay all our debts to God and to our fellow men, and finally, it obtains all kinds of graces for us from Almighty God.
The knowledge of Jesus Christ is the science of Christians and the science of salvation; Saint Paul says that it surpasses all human sciences in value and perfection.  This is true:
1. because of the dignity of its object, which is a God-man compared to Whom the whole universe is but a drop of dew or a grain of sand;
2. because of its helpfulness to us; human sciences, on the other hand, but fill us with the smoke and emptiness of pride;
3. and finally, because of its utter necessity: for no one can possibly be saved without the knowledge of Jesus Christ----and yet a man who knows absolutely nothing of any of the other sciences will be saved as long as he is illumined by the science of Jesus Christ.
Blessed is the Rosary which gives us this science and knowledge of our Blessed Lord through our meditations on His life, death, passion and glory.
The Queen of Saba, lost in admiration at Solomon's wisdom cried out: "Blessed are thy men and blessed are thy servants who stand before thee always, and hear thy wisdom."  But far
happier still are the faithful who carefully meditate on the life, virtues, suffering and glory of Our Savior, because by this means they can gain the perfect knowledge in which eternal life consists. "This is eternal life." 
Our Lady revealed to Blessed Alan that no sooner had Saint Dominic begun preaching the Rosary than hardened sinners were touched and wept bitterly over their grievous sins. Young children performed incredible penances and everywhere that he preached the Holy Rosary such fervor arose that sinners changed their lives and edified everyone by their penances and change of heart.
If by chance your conscience is burdened with sin, take your Rosary and say at least part of it, honoring some of the Mysteries of the life, passion or glory of Our Lord Jesus Christ, and be sure that, while you are meditating upon these Mysteries and honoring them He will show His sacred wounds to His Father in Heaven. He will plead for you and will obtain for you contrition and the forgiveness of your sins.
One day Our Lord said to Blessed Alan: "If only these poor wretched sinners would say My Rosary, they would share in the merits of My passion and I would be their Advocate and would appease My Father's Justice."
This life is nothing but warfare and a series of temptations; we do not have to contend with enemies of flesh and blood but with the very powers of Hell. What better weapons could we possibly use to combat them than the Prayer which our great Captain taught us, and the Angelic Salutation which has chased away devils, destroyed sin and renewed the world? What better weapon could we use than meditation on the life and passion of Our Lord and Savior Jesus Christ? For, as Saint Peter says, it is with this thought we must arm ourselves in order to defend ourselves against the very same enemies which he conquered and which molest us every day." 
"Ever since the devil was crushed by the humility and passion of Jesus Christ he has been very nearly unable to attack a soul that is armed with meditation on the mysteries of Our Lord's life, and, if he does trouble such a soul, he is sure to be shamefully defeated." (Cardinal Hughes.)
"Put you on the armor of God."  So arm yourselves with the arms of God----with the Holy Rosary----and you will crush the devil's head and you will stand firm in the face of all his temptations. This is why even the material rosary itself is such a terrible thing for the devil, and why the Saints have used it to enchain devils and to chase them out of the bodies of people who were possessed. Such happenings are reported in more than one authentic record.
Blessed Alan said that a man he knew of had desperately tried all kinds of devotions to rid himself of the evil spirit who possessed him, but without success. Finally he thought of wearing his Rosary around his neck, which eased him considerably. He discovered that whenever he took it off the devil tormented him cruelly, so he resolved to wear it night and day. This drove the evil spirit away forever, because he could not bear such a terrible chain. Blessed Alan also testified that he had delivered a large number of people who were possessed by putting the Rosary around their necks.
Father Jean Amat, of the Order of St. Dominic, was giving a series of Lenten sermons in the Kingdom of Aragon one year, when a young girl was brought to him who was possessed by the devil. After he had exorcised her several times without success he put his rosary around her neck. Hardly had he done so than the girl began to scream and yell in a fearful way, shrieking: "Take them off! Take them off! These beads are torturing me!" At last the Father, filled with pity for the girl, took his rosary off her.
The very next night when Father Amat was in bed, the same devils who had possession of the girl came to him foaming with rage and tried to seize him. But he had his rosary clasped in his hand and no efforts of theirs could wrench it from him. He managed to beat them with it very well indeed and chased them away, crying out: "Holy Mary, Our Lady of the Holy Rosary, come to my help!"
The next day when he went to the Church he met the poor girl----still possessed----and one of the devils within her started to laugh and said in a mocking voice: "Well, Brother, if you had been without your rosary, we should have made short shrift of you!" Then the good Father threw his rosary around the girl's neck without more ado and said: "By the sacred name of Jesus and that of Mary His Holy Mother, and by the power of the Most Holy Rosary I command you, evil spirits, to leave the body of this girl," and they were immediately forced to obey and she was delivered from them.
These stories show the power of the Holy Rosary in overcoming all possible temptations that evil spirits may bring----and also all kinds of sin----because these blessed beads put devils to rout.
1. Cf. Philipp. 3:8.
2. 3 Kings 10:8.
3. John 17:3.
4. Cf. 1 Peter 4:1.
5. Eph. 6:11.