@sacrumcoriesu
An excerpt from my longer post:
Immaculate Heart of Mary
….A defining expansion occurred during the Fátima apparitions of 1917, where Our Lady revealed that God wishes to establish in the world devotion to her Immaculate Heart. While the request for reparation was introduced in 1917, the specific First Saturday Devotion was formally established in 1925 when the Virgin Mary appeared to Sister Lucia in Pontevedra, Spain. This practice aims to make reparation for five specific types of blasphemies and ingratitude toward the Immaculate Heart.
In 1942, Pope Pius XII consecrated the world to the Immaculate Heart, and in 1944, he extended the feast to the universal Church. Today, the memorial is celebrated on the Saturday following the Solemnity of the Sacred Heart of Jesus.