What does the Church say about the liturgical memorial of Blessed Virgin Mary?

Madonna with Child Granducca.jpgThis most Holy Synod [Vatican II] deliberately teaches this
Catholic doctrine and at the same time admonishes all the sons of the Church
that the cult, especially the liturgical cult, of the Blessed Virgin, be
generously fostered, and the practices and exercises of piety, recommended by
the magisterium of the Church toward her in the course of centuries be made of
great moment, and those decrees, which have been given in the early days
regarding the cult of images of Christ, the Blessed Virgin and the saints, be
religiously observed. But it exhorts theologians and preachers of the
divine word to abstain zealously both from all gross exaggerations as well as
from petty narrow-mindedness in considering the singular dignity of the Mother
of God. Following the study of Sacred Scripture, the Holy Fathers, the
doctors and liturgy of the Church, and under the guidance of the Church’s
magisterium, let them rightly illustrate the duties and privileges of the
Blessed Virgin which always look to Christ, the source of all truth, sanctity
and piety. Let them assiduously keep away from whatever, either by word or
deed, could lead separated brethren or any other into error regarding the true
doctrine of the Church. Let the faithful remember moreover that true devotion
consists neither in sterile or transitory affection, nor in a certain vain
credulity, but proceeds from true faith, by which we are led to know the
excellence of the Mother of God, and we are moved to a filial love toward our
mother and to the imitation of her virtues. (Lumen gentium, 67)