13 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.).
Source: Ad Diem Illum Laetissimum (Vatican.va)