Mary

“Greetings, favored one! The Lord is with you... Do not be afraid, Mary, for you have found favor with God... Blessed are you among women, and blessed is the fruit of your womb."

Lk 1:28, 30; Lk 1:42; Lk 1:48 

1. Mother of God/Queen Mother (Ark of the New Covenant)

There is no affection due to Mary which is afforded beyond anything more than being the greatest of all Christian and the first to receive Christ. She is the woman, more than a vessel, through whose cooperation the Second person of the Trinity was made God-man. She is not God nor a deity, "praying" to her, just as with the rest of the saints, is only ever an indirect connection to God. This is mentioned in part on the previous page.

Sacred Scripture

Christology

Fr. John Hardon says, "Mary is truly Theotokos in two ways: she contributed everything 'to the formation of Christ's human nature that every other mother contributes to the fruit of her womb; and she conceived and bore the Second Person of the Trinity, not of course according to the divine nature but according to the human nature which the Logos assumed." (Read more here)

In addition to scripture, there really is not much left wanting in proving these titles/aspects of Mary as She relates to Christ. The facts from scripture are pretty straightforward that way. The hinge pin of this dogma, though, is Christ Himself. If we believe Christ is Divine with two natures one human and the other Divine, and we know the prophecy that Christ was to be born of a virgin and this Jesus is the Christ, then it is clear insofar as Jesus in His hypostatic union is God, Mary is the Mother of God.

It is important to note that though divinity and humanity are distinct in concept and hitherto in reality, but they are one in Christ, so all that is human genetically and biologically came from Mary, and arguably her fullness of nature which sin did not besmirch, His divinity though did not come from Mary. To claim that Divinity was imparted to Mary that she may produce something Divine would be to claim Mary as God and forget about the Holy Spirit in the equation. So it really is not Nestorianism to claim that what is human in Christ came from Mary, because they are joined in Him and that is make Mary Mother of God. If one claimed that Mary gave birth to something human and his divinity is not finally United to his humanity, that would be Nestorian. Jesus is God (hypostatically joined in humanity and the fullness of Divinity) and Son of Mary and Mary is the Mother of God, that is Catholicism. Christ was not implanted in the womb by the Holy Spirit or else he did not truly take on humanity, which would mean we could not be saved since He never assumed our nature. If we are saved by Christ, He is our brother and He was born of Mary who is both our Mothers.
"We confess, then, our Lord Jesus Christ, the unique Son of God, perfect God and perfect man, or a reasonable soul and body; begotten of the Father before (the) ages according to the Godhead, the same in the last days for us and for our salvation (born) of Mary the Virgin according to the manhood; the same consubstantial with the Father in the Godhead, and consubstantial with us in manhood, for a union of two natures took place; understanding of the unconfused union we confess the holy Virgin to be theotokos, because God the Word was made flesh and lived as man, and from the very conception united to himself the temple taken from her. As to the evangelical and apostolic phrases about the Lord, we knew that theologians treat some in common, as of one person, and distinguish others, as of two natures, and interpret the God-befitting ones in connection with the Godhead of Christ, and the humble ones of the manhood." Cyril of Alexandria

Magisterium

2. Conceived without Sin and Perpetually Free of sin (Immaculate Conception)

Sacred Scripture

Church Fathers/History

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Reasoning

Magisterium

3. The Perpetual Virginity

Sacred Scripture

Church Fathers/History

This dogma is taught by:

Magisterium

4. The Assumption

Sacred Scripture

Magisterium

Reasoning

Church Fathers/History

What makes this dogma essential to the Christian Faith?

The connection between Christ's identity and the New Covenant role of both Him and Mary is essential to the Christian faith, and this correlates directly to these dogmas. One may question whether the logical connection is close enough to constitute this sort of essential correlation. However, the sources consulted and the historical constancy of the Church on the matter testify to its legitimacy and therefore make up for whatever uncertainty one may feel. God is Love Itself, and it is unthinkable the vessel through which His Beloved is not only brought to Him but Saved, would merely be treated as another among the Beloved. Justice and Charity would both have it that the New Eve would have a primacy akin to though certainly not before Christ's. If Christ's flesh was first to enter eternity, it follows that she from whose flesh He received His (1) would be taken up with Him (4), preserved from all stain/corruption (2), and even perpetually virgin (3).