It was but fitting, therefore, that one day in the year should be set apart for this sacred duty: and what day could be more appropriate than the Friday of this week, which, though sacred to the Passion, admits the celebration of saints' feasts, as we have already noticed? As far back as the fifteenth century (that is, in the year 1423), we find the pious feast to be kept by his people. It was gradually introduced, and with the knowledge of the holy See, into several other countries; and at length, in the last century, Pope Benedict XIII, by a decree dated August 22, 1727, ordered it to be kept in the whole Church under the name of "the Feast of the Seven Dolours of the Blessed Virgin Mary", for, up to his time, it had gone under various names. We will explain the title thus given to it, as also the first origin of the devotion of the Seven Dolours, when our "Liturgical Year" brings us to the third Sunday of September [now celebrated on September 15], the second feast of Mary's Dolours. What the Church proposes to her children's devotion for this Friday in Passion-week, is that one special dolour of Mary -- her standing at the foot of the cross. Among the various titles given to this feast before it was extended by the holy See to the whole Church, we may mention, "Our Lady of Pity, "the Compassion of our Lady", and the one that was so popular throughout France, "Notre Dame de la Pamoison. These few historical observations prove that this feast was dear to the devotion of the people, even before it received the solemn sanction of the Church.
That we may clearly understand the object of this feast, and spend it, as the Church would have us do, in paying due honour to the Mother of God and of men, we must recall to our minds this great truth: that God, in the designs of His infinite wisdom, has willed that Mary should have a share in the work of the world's redemption. The mystery of the present feast is one of the applications of this divine law, a law which reveals to us the whole magnificence of God's plan; it is, also, one of the many realizations of the prophecy, that satan's pride was to be crushed by a women.
Text from the 'Liturgical Year' by Dom Gueranger