9 The beginnings of this regeneration and renovation of man are by Baptism. In this sacrament, when the unclean spirit has been expelled from the soul, the Holy Ghost enters in and makes it like to Himself. "That which is born of the Spirit, is spirit" (John iii., 6). The same Spirit gives Himself more abundantly in Confirmation, strengthening and confirming Christian life; from which proceeded the victory of the martyrs and the triumph of the virgins over temptations and corruptions. We have said that the Holy Ghost gives Himself: "the charity of God is poured out into our hearts by the Holy Ghost who is given to us" (Rom. v., 5). For He not only brings to us His divine gifts, but is the Author of them and is Himself the supreme Gift, who, proceeding from the mutual love of the Father and the Son, is justly believed to be and is called "Gift of God most High." To show the nature and efficacy of this gift it is well to recall the explanation given by the doctors of the Church of the words of Holy Scripture. They say that God is present and exists in all things, "by His power, in so far as all things are subject to His power; by His presence, inasmuch as all things are naked and open to His eyes; by His essence, inasmuch as he is present to all as the cause of their being." (St. Th. Ia, q. viii., a. 3). But God is in man, not only as in inanimate things, but because he ismore fully known and loved by him, since even by nature we spontaneously love,desire, and seek after the good. Moreover, God by grace resides in the just soulas in a temple, in a most intimate and peculiar manner. From this proceeds thatunion of affection by which the soul adheres most closely to God, more so thanthe friend is united to his most loving and beloved friend, and enjoys God inall fulness and sweetness. Now this wonderful union, which is properly called"indwelling," differing only in degree or state from that with whichGod beatifies the saints in heaven, although it is most certainly produced bythe presence of the whole Blessed Trinity-"We will come to Him and make ourabode with Him," (John xiv. 23.)-nevertheless is attributed in a peculiarmanner to the Holy Ghost. For, whilst traces of divine power and wisdom appeareven in the wicked man, charity, which, as it were, is the special mark of theHoly Ghost, is shared in only by the just. In harmony with this, the same Spiritis called Holy, for He, the first and supreme Love, moves souls and leads themto sanctity, which ultimately consists in the love of God. Wherefore the apostlewhen calling us to the temple of God, does not expressly mention the Father orthe Son, or the Holy Ghost: "Know ye not that your members are the templeof the Holy Ghost, who is in you, whom you have from God?" (1 Cor. vi. 19).The fullness of divine gifts is in many ways a consequence of the indwelling ofthe Holy Ghost in the souls of the just. For, as St. Thomas teaches, "whenthe Holy Ghost proceedeth as love, He proceedeth in the character of the firstgift; whence Augustine with that, through the gift which is the Holy Ghost, manyother special gifts are distributed among the members of Christ." (Summ.Th., la. q. xxxviii., a. 2. St. Aug. de Trin., xv., c. 19). Among these giftsare those secret warnings and invitations, which from time to time are excitedin our minds and hearts by the inspiration of the Holy Ghost. Without thesethere is no beginning of a good life, no progress, no arriving at eternalsalvation. And since these words and admonitions are uttered in the soul in anexceedingly secret manner, they are sometimes aptly compared in Holy Writ to thebreathing of a coming breeze, and the Angelic Doctor likens them to themovements of the heart which are wholly hidden in the living body. "Thy heart has a certain hidden power, and therefore the Holy Ghost, who invisibly vivifies and unites the Church, is compared to the heart." (Summ. Th. 3a, q. vii., a. I, ad 3). More than this, the just man, that is to say he who lives the life of divine grace, and acts by the fitting virtues as by means of faculties, has need of those seven gifts which are properly attributed to the Holy Ghost. By means of them the soul is furnished and strengthened so as to obey more easily and promptly His voice and impulse. Wherefore these gifts are of such efficacy that they lead the just man to the highest degree of sanctity; and of such excellence that they continue to exist even in heaven, though in a more perfect way. By means of these gifts the soul is excited and encouraged to seek after and attain the evangelical beatitudes, which, like the flowers that come forth in the spring time, are the signs and harbingers of eternal beatitude. Lastly there are those blessed fruits, enumerated by the Apostle (Gal. v., 22), which the Spirit, even in this mortal life, produces and shows forth in the just; fruits filled with all sweetness and joy, inasmuch as they proceed from the Spirit, "who is in the Trinity the sweetness of both Father and Son, filling all creatures with infinite fullness and profusion." (St. Aug. de Trin. 1. vi., c. 9). The Divine Spirit, proceeding from the Father and the Word in the eternal light of sanctity, Himself both Love and Gift, after having manifested Himself through the veils of figures in the Old Testament, poured forth all his fullness upon Christ and upon His mystic Body, the Church; and called back by his presence and grace men who were going away in wickedness and corruption with such salutary effect that, being no longer of the earth earthy, they relished and desired quite other things, becoming of heaven heavenly.
Source: Divinum Illud Munus (Vatican.va)