St. Mary Major is important to Christendom for three reasons:
(a) It stands as a venerable monument to the Council of Ephesus (431), at which the dogma of Mary's divine Motherhood was solemnly defined; the definition of the Council occasioned a most notable increase in the veneration paid to Mary.
(b) The basilica is Rome's "church of the crib," a kind of Bethlehem within the Eternal City; it also is a celebrated station church, serving, for instance, as the center for Rome's liturgy for the first Mass on Christmas. In some measure every picture of Mary with the divine Child is traceable to this church.
(c) St. Mary Major is Christendom's first Marian shrine for pilgrims. It set the precedent for the countless shrines where pilgrims gather to honor our Blessed Mother throughout the world. Here was introduced an authentic expression of popular piety that has been the source of untold blessings and graces for Christianity in the past as in the present.
Information is from the Canon Regulars of St. John Cantius:
On the Esquiline Hill, not far from St. Peter in Chains, towers the Basilica of St. Mary Major.
If Grandiose, both in its exterior and in it interior, the Basilica was erected by Pope Sixtus III (432-440), one year after the proclamation by the Council of Ephesus of the dogma of Theotokos—Mary, Mother of God. Before being called "St. Mary Major," the ancient Romans had called it the Basilica Liberii (back to Pope Liberius (352-366). In August 352, Pope Liberius experience a vision of Our Lady and it was She, who traced out the dimensions of this church. Pope Liberius then saw with his own eyes the area of land covered in snow on which the church was to be built.
This Basilica also contains the revered image of the Madonna of St. Luke, called Salus Populi Romani.
How have I kept the first eight days of Lent? Surely, as "the glory of the Lord dwelt upon Sinai" and upon Moses, so the "right hand of His Majesty" was extended over us during the past week.
Let us pray: Graciously look down, O Lord, we beseech Thee, upon the devotion of Thy people, that they, who are mortified in body by abstinence, may be refreshed in mind through the fruit of good works. Through Christ, Our Lord. Amen.