Let’s go into this using something I got together earlier, maybe making a different point, but has useful documents cited:
The Catechism states that when Our Lady gave birth to Jesus, she gave birth to all the members of the Church.
The Vatican II documents state that at Pentecost, the Church is ‘sanctified’; that Jesus gave us the Holy Spirit, that He might remain with us; that ‘…the “Acts of the Apostles” began with Pentecost, just as Christ was conceived in the Virgin Mary’.
The Part One ‘The Professional of Faith’ (Section Two) of the Catechism, we read: 'In her, the “wonders of God” that the Spirit was to fulfill in Christ and the Church began to be manifested…722
The Holy Spirit prepared Mary by his grace. It was fitting that the mother of him in whom "the whole fullness of deity dwells bodily"102 should herself be “full of grace.”’
In Ineffabilis Deus, we are told: ‘…the Roman Pontiffs…denounced as false and absolutely foreign to the mind of the Church the opinion of those who held and affirmed that it was not the conception of the Virgin but her sanctification that was honored by the Church. They never thought that greater leniency should be extended toward those who, attempting to disprove the doctrine of the Immaculate Conception of the Virgin, devised a distinction between the first and second instance of conception and inferred that the conception which the Church celebrates was not that of the first instance of conception but the second. In fact, they held it was their duty not only to uphold and defend with all their power the Feast of the Conception of the Blessed Virgin but also to assert that the true object of this veneration was her conception considered in its first instant.’
'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.’
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