31 But if our Savior, by His death, became, in the full and complete sense of the word, the Head of the Church, it was likewise through His blood that the Church was enriched with the fullest communication of the Holy Spirit, through which, from the time when the Son of Man was lifted up and glorified on the Cross by His sufferings, she is divinely illumined. For then, as Augustine notes, with the rending of the veil of the temple it happened that the dew of the Paraclete's gifts, which heretofore had descended only on the fleece, that is on the people of Israel, fell copiously and abundantly (while the fleece remained dry and deserted) on the whole earth, that is on the Catholic Church, which is confined by no boundaries of race or territory. Just as at the first moment of the Incarnation the Son of the Eternal Father adorned with the fullness of the Holy Spirit the human nature which was substantially united to Him, that it might be a fitting instrument of the Divinity in the sanguinary work of the Redemption, so at the hour of His precious death He willed that His Church should be enriched with the abundant gifts of the Paraclete in order that in dispensing the divine fruits of the Redemption she might be, for the Incarnate Word, a powerful instrument that would never fail. For both the juridical mission of the Church, and the power to teach, govern and administer the Sacraments, derive their supernatural efficacy and force for the building up of the Body of Christ from the fact that Jesus Christ, hanging on the Cross, opened up to His Church the fountain of those divine gifts, which prevent her from ever teaching false doctrine and enable her to rule them for the salvation of their souls through divinely enlightened pastors and to bestow on them an abundance of heavenly graces.
Source: Mystici Corporis Christi (Vatican.va)