Christians have sometimes based a belief in our Lady's Assumption upon her perpetual virginity; or her freedom from actual sin; or her freedom from original sin; or the inseparable physical bond between her and the Son who shared her flesh and blood, her DNA [a point essentially made by Dom Gueranger]; or the unbreakable bond of love that must exist between Mother and Son. All this I agree with. But as I observed yesterday, the reason most consonant with the liturgical traditions of East and West is that she was assumed so that she could be our Intercessor. Sometimes it is considered that the concept of our Lady Mediatrix of All Graces is somehow "extreme" and is a horribly divisive extravagance that any sensible ecumenist (oxymoron?) dreads being defined ex cathedra by some maximalising pope. I disagree. I will make the point by giving a translation of a Secret which was often used in many parts of Europe during this season - including England.
O Lord, may the prayer of the Mother of God commend our offerings before thy merciful kindness; for thou didst translate her from this present Age for this purpose, that (idcirco ... ut) she might confidently (fiducialiter) intercede before thee for our sins.
A considerable Russian theologian, Vladimir Lossky, explained that "freed from the limitations of time, Mary can be the cause of that which is before her; can preside over that which comes after her. She obtains eternal benefits. It is through her that men and angels receive grace. No gift is received in the Church without the assistance of the Mother of God, who is herself the first-fruits of the glorified Church. Thus, having attained to the limits of becoming, she necessarily watches over the destinies of the Church and of the universe".
Our Lady was assumed that she might be the treasury of God's grace, the Mediatrix of All Graces, the mother whose hands stretch out to bestow. In Newman's majestic words, written while he was still an Anglican: There was a wonder in heaven; a throne was seen, far above all created powers, mediatorial, intercessory; a title archetypical; a crown bright as the morning star; a glory issuing from the Eternal Throne; robes as pure as the heavens; and a sceptre over all ... The vision is found in the Apocalypse, a Woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars.
A well-known Roman Catholic (traditionalist) scholar once said to me that he felt Newman wrote better when he was an Anglican than when he was a Roman Catholic. This passage could stand as evidence. When Newman was beatified, the author of his Anglican writings was beatified too. Nobody is more Patrimonial than Newman.