Our Lady, conceived without sin,

Pray for us who have recourse to thee!

Baptisty Ceiling, S.Maria Maggiore

Given that this is the 40th Anniversary of the closing of the Second Vatican Council, it seems fitting to re-read some of what the Second Vatican Council had to say about our Lady.

Lumen Gentium 65.:

But while in the most holy Virgin the Church has already reached
that perfection whereby she is without spot or wrinkle, the followers of Christ
still strive to increase in holiness by conquering sin. And so they turn
their eyes to Mary who shines forth to the whole community of the elect as the
model of virtues. Piously meditating on her and contemplating her in the light
of the Word made man, the Church with reverence enters more intimately into the
great mystery of the Incarnation and becomes more and more like her Spouse. For
Mary, who since her entry into salvation history unites in herself and re-echoes
the greatest teachings of the faith as she is proclaimed and venerated, calls
the faithful to her Son and His sacrifice and to the love of the Father. Seeking
after the glory of Christ, the Church becomes more like her exalted Type, and
continually progresses in faith, hope and charity, seeking and doing the will of
God in all things. Hence the Church, in her apostolic work also, justly looks to
her, who, conceived of the Holy Spirit, brought forth Christ, who was born of
the Virgin that through the Church He may be born and may increase in the hearts
of the faithful also. The Virgin in her own life lived an example of that
maternal love, by which it behooves that all should be animated who cooperate in
the apostolic mission of the Church for the regeneration of men.

The council itself didn't formulate any formal Marian dogmas (although Paul VI did declare her 'Mother of the Church'), but this understanding of the Church in the light of Mary and Mary in the light of the Church is a very rich point to reflect on. She is not greater than the Church, because she is a member of it, but she is the greatness of the Church in that in her is fulfilled all that the Church promises. She is the type and model of the Church in that she comes before the Church and foreshadows it; she is the fulfillment of the Church in her purity and in her Assumption.