12 Moreover it was not only the prerogative of the Most Holy Mother to have furnished the material of His flesh to the Only Son of God, Who was to be born with human members (S. Bede Ven. L. Iv. in Luc . xl.), of which material should be prepared the Victim for the salvation of men; but hers was also the office of tending and nourishing that Victim, and at the appointed time presenting Him for the sacrifice. Hence that uninterrupted community of life and labors of the Son and the Mother, so that of both might have been uttered the words of the Psalmist"My life is consumed in sorrow and my years in groans" ( Ps xxx., 11). When the supreme hour of the Son came, beside the Cross of Jesus there stood Mary His Mother, not merely occupied in contemplating the cruel spectacle, but rejoicing that her Only Son was offered for the salvation of mankind, and so entirely participating in His Passion, that if it had been possible she would have gladly borne all the torments that her Son bore (S. Bonav. 1. Sent d. 48, ad Litt. dub . 4). And from this community of will and suffering between Christ and Mary she merited to become most worthily the Reparatrix of the lost world (Eadmeri Mon. De Excellentia Virg. Mariae , c. 9) and Dispensatrix of all the gifts that Our Savior purchased for us by His Death and by His Blood.
Source: Ad Diem Illum Laetissimum (Vatican.va)