24 Leaving aside charity towards God, who can contemplate the Immaculate Virgin without feeling moved to fulfill that precept which Christ called peculiarly His own, namely that of loving one another as He loved us? "A great sign," thus the Apostle St. John describes a vision divinely sent him, appears in the heavens: "A woman clothed with the sun, and with the moon under her feet and a crown of twelve stars upon her head" ( Apoc . xii., 1). Everyone knows that this woman signified the Virgin Mary, the stainless one who brought forth our Head. The Apostle continues: "And, being with child, she cried travailing in birth, and was in pain to be delivered" ( Apoc . xii., 2). John therefore saw the Most Holy Mother of God already in eternal happiness, yet travailing in a mysterious childbirth. What birth was it? Surely it was the birth of us who, still in exile, are yet to be generated to the perfect charity of God, and to eternal happiness. And the birth pains show the love and desire with which the Virgin from heaven above watches over us, and strives with unwearying prayer to bring about the fulfillment of the number of the elect.
Source: Ad Diem Illum Laetissimum (Vatican.va)