The Congregation was founded "to witness in the Church and in the world that God continues to be faithful in his love for the Jewish people and to hasten the fulfilment of the promises concerning the Jews and the Gentiles." (Const. 2)

Theodore Ratisbonne was born in Strasbourg in 1802 into a Jewish family that was in the process of being assimilated. He grew up in an atmosphere of learning and affection, where religion did not, however, play a significant part. "Religion was repugnant to me, my own and all other religions." One day this prayer arose out of his confusion: "Oh God, if you really exist, let me know the truth, and I swear to consecrate my life to it."

The teaching of a young philosophy professor, Louis Bautain, who drew on the Scriptures in his studies, gradually set Theodore on the path of discovery of the God of the Old and New Testaments. He was baptized at the age of 24 on Holy Saturday, 14 April 1827 by Louise Humann. Throughout his life as a Christian, and later as a priest, the Word of God inspired him and called him to apostolic life, a call that was to be fulfilled only 15 years later.

On 20 January 1842, his younger brother Alphonse also decided to become a Christian after Mary appeared to him in a vision in Rome. In the light of the Word of God, Theodore was able to interpret this sign from Mary and, encouraged by his brother, founded the congregation of Our Lady of Sion in 1843. In 1852, he gathered together the first small group of what was to become the men's Congregation of the Religious of Our Lady of Sion.