Mystici Corporis Christi §56

⁵⁶ If we examine closely this divine principle of life and power given by Christ, insofar as it constitutes the very source of every gift and created grace, we easily perceive that it is nothing else than the Holy spirit, the Paraclete, who proceeds from the Father and the Son, and who is called in a special way, the "Spirit of Christ" or the "Spirit of the Son." For it was by this Breath of grace and truth that the Son of God anointed His soul in the immaculate womb of the Blessed Virgin; this Spirit delights to dwell in the beloved soul of our Redeemer as in His most cherished shrine; this Spirit Christ merited for us on the Cross by shedding His Own Blood; this Spirit He bestowed on the Church for the remission of sins, when He breathed on the Apostles; and while Christ alone received this Spirit without measure, to the members of the Mystical Body He is imparted only according to the measure of the giving of Christ from Christ's own fulness. But after Christ's glorification on the Cross, His Spirit is communicated to the Church in an abundant outpouring, so that she, and her individual members, may become daily more and more like to our Savior. It is the Spirit of Christ that has made us adopted sons of God in order that one day "we all beholding the glory of the Lord with open face may be transformed into the same image from glory to glory."