My favorite excerpt of the bull of promulgation of the Dogma of the Immaculate Conception, "Ineffabilis Deus"

Apostolic Constitution issued by Pope Pius IX on December 8, 1854.

Interpreters of the Sacred Scripture

The Fathers and writers of the Church, well versed in the heavenly Scriptures, had nothing more at heart than to vie with one another in preaching and teaching in many wonderful ways the Virgin's supreme sanctity, dignity, and immunity from all stain of sin, and her renowned victory over the most foul enemy of the human race.

This they did in the books they wrote to explain the Scriptures, to vindicate the dogmas, and to instruct the faithful.

These ecclesiastical writers in quoting the words by which at the beginning of the world God announced his merciful remedies prepared for the regeneration of mankind -- words by which he crushed the audacity of the deceitful serpent and wondrously raised up the hope of our race, saying, "I will put enmities between you and the woman, between your seed and her seed"[13] -- taught that by this divine prophecy the merciful Redeemer of mankind, Jesus Christ, the only begotten Son of God, was clearly foretold: That his most Blessed Mother, the Virgin Mary, was prophetically indicated; and, at the same time, the very enmity of both against the evil one was significantly expressed.

Hence, just as Christ, the Mediator between God and man, assumed human nature, blotted the handwriting of the decree that stood against us, and fastened it triumphantly to the cross, so the most holy Virgin, united with him by a most intimate and indissoluble bond, was, with him and through him, eternally at enmity with the evil serpent, and most completely triumphed over him, and thus crushed his head with her immaculate foot.[14]

This sublime and singular privilege of the Blessed Virgin, together with her most excellent innocence, purity, holiness and freedom from every stain of sin, as well as the unspeakable abundance and greatness of all heavenly graces, virtues and privileges -- these the Fathers beheld in that ark of Noah, which was built by divine command and escaped entirely safe and sound from the common shipwreck of the whole world;

[15] in the ladder which Jacob saw reaching from the earth to heaven, by whose rungs the angels of God ascended and descended, and on whose top the Lord himself leaned'

[16] in that bush which Moses saw in the holy place burning on all sides, which was not consumed or injured in any way but grew green and blossomed beautifully;

[17] in that impregnable tower before the enemy, from which hung a thousand bucklers and all the armor of the strong;

[18] in that garden enclosed on all sides, which cannot be violated or corrupted by any deceitful plots;

[19] as in that resplendent city of God, which has its foundations on the holy mountains;

[20] in that most august temple of God, which, radiant with divine splendors, is full of the glory of God;

[21] and in very many other biblical types of this kind. In such allusions the Fathers taught that the exalted dignity of the Mother of God, her spotless innocence and her sanctity unstained by any fault, had been prophesied in a wonderful manner.

In like manner did they use the words of the prophets to describe this wondrous abundance of divine gifts and the original innocence of the Virgin of whom Jesus was born.

They celebrated the august Virgin as the spotless dove, as the holy Jerusalem, as the exalted throne of God, as the ark and house of holiness which Eternal Wisdom built, and as that Queen who, abounding in delights and leaning on her Beloved, came forth from the mouth of the Most High, entirely perfect, beautiful, most dear to God and never stained with the least blemish.