Encyclical of Pope Pius X on the Immaculate Conception, 2 February 1904.
Mary, Mother of God and Men: sections 10-14
For is not Mary the Mother of Christ? Then she is our Mother also. And we must in truth hold that Christ, the Word made Flesh, is also the Savior of mankind. He had a physical body like that of any other man: and again as Savior of the human family, he had a spiritual and mystical body, the society, namely, of those who believe in Christ. "We are many, but one sole body in Christ" (Rom. xii., 5). Now the Blessed Virgin did not conceive the Eternal Son of God merely in order that He might be made man taking His human nature from her, but also in order that by means of the nature assumed from her He might be the Redeemer of men. For which reason the Angel said to the Shepherds: "To-day there is born to you a Savior who is Christ the Lord" (Luke ii., 11).
Wherefore in the same holy bosom of his most chaste Mother Christ took to Himself flesh, and united to Himself the spiritual body formed by those who were to believe in Him. Hence Mary, carrying the Savior within her, may be said to have also carried all those whose life was contained in the life of the Savior. Therefore all we who are united to Christ, and as the Apostle says are members of His body, of His flesh, and of His bones (Ephes. v., 30), have issued from the womb of Mary like a body united to its head. Hence, though in a spiritual and mystical fashion, we are all children of Mary, and she is Mother of us all. Mother, spiritually indeed, but truly Mother of the members of Christ, who are we (S. Aug., L. de S. Virginitate, c. 6).
If then the most Blessed Virgin is the Mother at once of God and men, who can doubt that she will work with all diligence to procure that Christ, Head of the Body of the Church (Coloss. i., 18), may transfuse His gifts into us, His members, and above all that of knowing Him and living through Him (I John iv., 9)?
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.
It cannot, of course, be denied that the dispensation of these treasures is the particular and peculiar right of Jesus Christ, for they are the exclusive fruit of His Death, who by His nature is the mediator between God and man. Nevertheless, by this companionship in sorrow and suffering already mentioned between the Mother and the Son, it has been allowed to the august Virgin to be the most powerful mediatrix and advocate of the whole world with her Divine Son (Pius IX, Ineffabilis).
The source, then, is Jesus Christ "of whose fullness we have all received" (John i., 16), "from whom the whole body, being compacted and fitly joined together by what every joint supplieth, according to the operation in the measure of every part, maketh increase of the body unto the edifying of itself in charity" (Ephesians iv., 16). But Mary, as St. Bernard justly remarks, is the channel (Serm. de temp on the Nativ. B. V. De Aquaeductu n. 4); or, if you will, the connecting portion the function of which is to join the body to the head and to transmit to the body the influences and volitions of the head--We mean the neck. Yes, says St. Bernardine of Sienna, "she is the neck of Our Head, by which He communicates to His mystical body all spiritual gifts" (Quadrag. de Evangel. aetern. Serm. x., a. 3, c. iii.).
We are then, it will be seen, very far from attributing to the Mother of God a productive power of grace--a power which belongs to God alone. Yet, since Mary carries it over all in holiness and union with Jesus Christ, and has been associated by Jesus Christ in the work of redemption, she merits for us de congruo, in the language of theologians, what Jesus Christ merits for us de condigno, and she is the supreme Minister of the distribution of graces. Jesus "sitteth on the right hand of the majesty on high" (Hebrews i. 3.). Mary sitteth at the right hand of her Son--a refuge so secure and a help so trusty against all dangers that we have nothing to fear or to despair of under her guidance, her patronage, her protection. (Pius IX, in Bull Ineffabilis).
[De congruo: It is in some way fitting that Mary's action be rewarded by the redemption of mankind, but this gift of redemption surpasses the worth of her action; De condigno: Christ's action is by itself worthy to be rewarded by the redemption of all men, and in fact far surpasses what was necessary to accomplish that redemption with complete justice.]
Excerpted from Pope Pius X's Encyclical on the Immaculate Conception, Ad diem illum laetissimum, 2 November 1904