51 Holiness begins from Christ; and Christ is its cause. For no act conducive to salvation can be performed unless it proceeds from Him as from its supernatural source. "Without me," He says, "you can do nothing." If we grieve and do penance for our sins if, with filial fear and hope, we turn again to God, it is because He is leading us. Grace and glory flow from His inexhaustible fulness. Our Savior is continually pouring out His gifts of counsel, fortitude, fear and piety, especially on the leading members of His Body, so that the whole Body may grow ever more and more in holiness and integrity of life. When the Sacraments of the Church are administered by external rite, it is He who produces their effect in souls. He nourishes the redeemed with His own flesh and blood and thus calms the turbulent passions of the soul; He gives increase of grace and prepares future glory for souls and bodies. All these treasures of His divine goodness He is said to bestow on the members of His Mystical Body, not merely because He, as the Eucharistic Victim on earth and the glorified Victim in heaven, through His wounds and His prayers pleads our cause before the Eternal Father, but because He selects, He determines, He distributes every single grace to every single person "according to the measure of the giving of Christ." Hence it follows that from our Divine Redeemer as from a fountainhead "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, into the edifying of itself in charity."
Source: Mystici Corporis Christi (Vatican.va)