Margaret Mary Alocoque was born at Verosvres in the diocese of Autun in 1647. When only three years old she already had the greatest fear of the smallest sin. Indeed, the very word “sin” frightened her exceedingly. And before she was quite four years of age, without anyone suggesting them to her, she clearly pronounced the words, “O my God, I consecrate my purity to Thee, for my whole life: I vow to Thee perpetual chastity.”
Even as a mere tot she loved Jesus and Mary above all things; and as soon as she had learned to say the rosary, she recited it every day. Some time after she had made her First Holy Communion, God sent her a grievous sickness that lasted four years. The Margaret had recourse to Our Lady. She promised that if that dear Mother would cure her she would become a Sister. Scarcely had she uttered the words, when she was cured. After some hesitation she entered the Order of the Visitation of Paray-le-Monial at the age of twenty-three. The Sacred Heart of Jesus manifested itself to her several times; through her He willed to make this devotion known to the world. She died October 7, 1690. She was canonized by Pope Benedict XV on Ascenion Thursday, May 13, 1920. Pius XI extended her feast to the whole Church on June 28, 1929.
(Source: The New Roman Missal, Rev. F. X. Lasance)