From the writings of St. Louis de Montfort (1673-1716):
A nobleman who had several daughters entered one of them in a lax monastery where the nuns were very proud and thought of nothing else but worldly pleasures. The nuns’ confessor, on the other hand, was a zealous priest and had a great love for the Holy Rosary. Wishing to guide this nun into a better way of life he ordered her to say the Rosary every day in honor of the Blessed Virgin while meditating on the life, passion and glory of Jesus Christ.
She joyously undertook to say the Rosary and little by little she grew to have a repugnance for the wayward habits of her sisters in religion. She developed a love for silence and prayer and this in spite of the fact that the others despised and ridiculed her and called her a fanatic. It was at this time that a holy priest, who was making the visitation of the convent, had a strange vision while he was making his meditation: he saw a nun in her room, rapt in prayer, kneeling in front of a Lady of breathless beauty who was surrounded by Angels. The latter had flaming spears with which they repelled a crowd of devils who wanted to come in. These evil spirits then fled to the other nuns’ rooms under the guise of vile animals.
By this vision the priest became aware of the lamentable state the monastery was in and he was so upset that he thought he might almost die of grief. He immediately sent for the young religious and exhorted her to persevere.
As he pondered on the value of the Rosary, he decided to try to reform the sisters by means of it. He bought a supply of beautiful rosaries and gave one to each nun, imploring them to say the Rosary every day, even going so far as to promise them that, if they would only say it faithfully, he would not try to force them to alter their lives. Wonderful and strange as it may seem the nuns agreed to this pact and were glad to be given the rosaries and promised to say them.
Little by little they began to give up their empty and worldly pursuits, letting silence and recollection come into their lives. In less than a year they all asked that the monastery be reformed.
So the Holy Rosary worked more changes in their hearts than the priest could have worked by exhorting and commanding them.
— The Secret of the Rosary