On 1st November 1950, Pope Pius XII published the Apostolic Constitution Munificentissimus Deus in which he declared that Our Lady had been assumed body and soul into Heaven at the end of her life here on earth. This was no new teaching, as the Irish bishops reminded their faithful in the run-up to the declaration; they recalled that the Irish people, along with the other peoples of the world, had long held this belief of Our Lady’s Assumption. Here is the central excerpt from Munificentissimus Deus:
We rejoice greatly that this solemn event falls, according to the design of God’s providence, during this Holy Year, so that we are able, while the great Jubilee is being observed, to adorn the brow of God’s Virgin Mother with this brilliant gem, and to leave a monument more enduring than bronze of our own most fervent love for the Mother of God.
For which reason, after we have poured forth prayers of supplication again and again to God, and have invoked the light of the Spirit of Truth, for the glory of Almighty God who has lavished his special affection upon the Virgin Mary, for the honor of her Son, the immortal King of the Ages and the Victor over sin and death, for the increase of the glory of that same august Mother, and for the joy and exultation of the entire Church; by the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.
Hence if anyone, which God forbid, should dare willfully to deny or to call into doubt that which we have defined, let him know that he has fallen away completely from the divine and Catholic Faith.
In order that this, our definition of the bodily Assumption of the Virgin Mary into heaven may be brought to the attention of the universal Church, we desire that this, our Apostolic Letter, should stand for perpetual remembrance, commanding that written copies of it, or even printed copies, signed by the hand of any public notary and bearing the seal of a person constituted in ecclesiastical dignity, should be accorded by all men the same reception they would give to this present letter, were it tendered or shown.
It is forbidden to any man to change this, our declaration, pronouncement, and definition or, by rash attempt, to oppose and counter it. If any man should presume to make such an attempt, let him know that he will incur the wrath of Almighty God and of the Blessed Apostles Peter and Paul.
Saint Alphonsus de Ligouri wrote a discourse on the Assumption of Our Lady in The Glories of Mary. In it, he says:
Let us rejoice with Mary in the glory with which God has enriched her; and let us also rejoice for ourselves, for Mary, at the same time was made queen of the world, and appointed our advocate. She is so merciful an advocate, that she consents to defend all sinners who recommend themselves to her; and she is so powerful with our Judge that she gains all the causes which she defends. Oh our queen and advocate, in thy hand is our salvation; if thou dost pray for us, we shall be saved. Say to thy Son that thou dost wish us with thee in paradise. He denies thee nothing that thou dost ask. Oh our life, our sweetness, and our hope ! Mary, pray to Jesus for us.