Although it falls on a Saturday this year, the obligation to attend Mass is not lifted (as with other Holy Days) for the Feast of the Immaculate Conception on December 8. Thus, Catholics must attend Mass for the Holy Day (either the Friday night vigil or Saturday) and again that weekend for their Sunday obligation (either the Saturday night vigil or on Sunday).
The Immaculate Conception of Mary, the Mother of Jesus, is the belief that God preserved Mary from any inclination to sin, the inheritance of original sin passed on to all mankind from Adam and Eve. The feast of the Conception of Mary appeared in the Roman calendar in 1476. After the dogmatic definition by Pope Pius IX in 1854, it became the Feast of the Immaculate Conception.
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