Through the merits of her Divine Son, foreseen by Almighty God, the blessed Virgin Mary was conceived without the stain of original sin, in which all other s of the children of Adam are born. This singular grace bestowed upon our Lady, was revealed by God to the holy Apostles, and by them handed down to the Church. The truth of the Immaculate Conception was finally and infallibly declared, or defined, by Pope Pius IX, in the year 1854, and from that date it has been an article of the Catholic Faith. The celebration of a Festival in honour of this mystery, may be traced back for about a thousand years. It is now not only of obligatory celebration everywhere, but ranks liturgically among the chief solemnities of the Ecclesiastical year.
And here is a recording of the Chant Offertory for today's feast in the Extraordinary Form.
Ave Maria, gratia plena, Dominus tecum. Benedicta tu in mulieribus. Alleluia.
Hail Mary, full of grace, the Lord is with thee; blessed art thou amongst women, alleluia.