“The Order of Grace” can be explained by recalling the Blessed Virgin Mary’s life.
The Second Vatican Council document The Light of the Nations (Lumen Gentium) explains the order of grace through the Blessed Virgin Mary in this way:
“Predestined from eternity by that decree of divine providence which determined the incarnation of the Word to be the Mother of God, the Blessed Virgin was on this earth the virgin Mother of the Redeemer, and above all others and in a singular way, the generous associate and humble handmaid of the Lord. She conceived, brought forth and nourished Christ. She presented Him to the Father in the temple, and was united with Him by compassion as He died on the Cross. In this singular way she cooperated by her obedience, faith, hope and burning charity in the work of the Savior in giving back supernatural life to souls. Wherefore she is our mother in the order of grace. This maternity of Mary in the order of grace began with the consent which she gave in faith at the Annunciation and which she sustained without wavering beneath the Cross, and lasts until the eternal fulfillment of all the elect.”1
The Motherhood of the Blessed Virgin Mary was not only physical to Jesus, but also spiritual to the Church, the Mystical Body of Christ.2 At the Foot of the Cross, our Lady received her pangs of birth spiritually, when the Church was born from the side of Christ.3
1) Vatican II, Lumen Gentium, 61-62
2) cf. Pope St. Pius X, Ad Diem Illum Laetissimum, 10 13) cf. Sacramentary of Masses of the Blessed Virgin Mary, Votive Mass in honor of Mary at the Foot of the Cross II, Preface II, 117
3) cf. Sacramentary of Masses of the Blessed Virgin Mary, Votive Mass in honor of Mary at the Foot of the Cross II, Preface II, 117