Our Lady roped him with her rosary

The great secret of Saint Louis Marie de Montfort on how to attract souls and give them to Jesus is Marian devotion. He founded everything he did on her, he leaned on her, and he could not find a more effective weapon in his time.

In contrast to the joyless austerity, the dark terror and the arrogant rigorism of Jansenism, he proposed the filial, trusting, fervent, all-embracing and efficacious love of the devout servant of Mary, the Refuge of Sinners, the Mother of Divine Grace, our life, our sweetness, and our hope…

She is also our advocate—an intermediary between God and the sinner—who is busy invoking the clemency of the judge so that He bends His justice, and touching the obstinate hearts of the guilty.

In his conviction and experience of this role of Mary, the missionary declared in his colorful simplicity that "never has a sinner resisted her, once she has roped him with her rosary." True devotion to Our Lady—based on Church tradition as well as Christian and Catholic common sense—primarily tends towards union with Jesus, under the guidance of His Mother…

And that is why, dear sons and daughters, we fervently wish that, over and above the various manifestations of piety towards the Mother of God, Mother of mankind, all of you may draw from the treasure of our saint's writings and examples of what formed the basis of his Marian devotion—his firm conviction of Mary's most powerful intercession, his firm will to imitate as much as possible the virtues of the Virgin of Virgins, and the vehement ardor of his love for Jesus and His Mother.

Pius XII, speech to the pilgrims gathered in Rome for the beatification of St Louis Marie de Montfort, July 21, 1947 (excerpts)