The Holy Spirit Twice Given by Christ. The Procession of the Holy Spirit from the Father and from the Son is Apart from Time, Nor Can He Be Called the Son of Both
Further, in that Highest Trinity which is God, there are no intervals of time, by which it could be shown, or at least inquired, whether the Son was born of the Father first and then afterwards the Holy Spirit proceeded from both; since Holy Scripture calls Him the Spirit of both. For it is He of whom the apostle says, “But because you are sons, God has sent forth the Spirit of His Son into your hearts:” and it is He of whom the same Son says, “For it is not ye who speak, but the Spirit of your Father who speaks in you.” And it is proved by many other testimonies of the Divine Word, that the Spirit, who is specially called in the Trinity the Holy Spirit, is of the Father and of the Son: of whom likewise the Son Himself says, “Whom I will send unto you from the Father;” and in another place, “Whom the Father will send in my name.” And we are so taught that He proceeds from both, because the Son Himself says, He proceeds from the Father. And when He had risen from the dead, and had appeared to His disciples, “He breathed upon them, and said, Receive the Holy Ghost,” so as to show that He proceeded also from Himself. And Itself is that very “power that went out from Him,” as we read in the Gospel, “and healed them all.”
46. But the reason why, after His resurrection, He both gave the Holy Spirit, first on earth, and afterwards sent Him from heaven, is in my judgment this: that “love is shed abroad in our hearts,” by that Gift itself, whereby we love God and our neighbors, according to those two commandments, “on which hang all the law and the prophets.” And Jesus Christ, in order to signify this, gave to them the Holy Spirit, once upon earth, on account of the love of our neighbor, and a second time from heaven, on account of the love of God. And if some other reason may perhaps be given for this double gift of the Holy Spirit, at any rate we ought not to doubt that the same Holy Spirit was given when Jesus breathed upon them, of whom He by and by says, “Go, baptize all nations in the name of the Father, and of the Son, and of the Holy Spirit,” where this Trinity is especially commended to us. It is therefore He who was also given from heaven on the day of Pentecost, i.e. ten days after the Lord ascended into heaven. How, therefore, is He not God, who gives the Holy Spirit? Nay, how great a God is He who gives God! For no one of His disciples gave the Holy Spirit, since they prayed that He might come upon those upon whom they laid their hands: they did not give Him themselves. And the Church preserves this custom even now in the case of her rulers. Lastly, Simon Magus also, when he offered the apostles money, does not say, “Give me also this power, that I may give” the Holy Spirit; but, “that on whomsoever I may lay my hands, he may receive the Holy Spirit.” Because neither had the Scriptures said before, And Simon, seeing that the apostles gave the Holy Spirit; but it had said, “And Simon, seeing that the Holy Spirit was given by the laying on of the apostles' hands.” Therefore also the Lord Jesus Christ Himself not only gave the Holy Spirit as God, but also received it as man, and therefore He is said to be full of grace, and of the Holy Spirit. And in the Acts of the Apostles it is more plainly written of Him, “Because God anointed Him with the Holy Spirit.” Certainly not with visible oil but with the gift of grace which is signified by the visible ointment wherewith the Church anoints the baptized. And Christ was certainly not then anointed with the Holy Spirit, when He, as a dove, descended upon Him at His baptism. For at that time He deigned to prefigure His body, i.e. His Church, in which especially the baptized receive the Holy Spirit. But He is to be understood to have been then anointed with that mystical and invisible unction, when the Word of God was made flesh, i.e. when human nature, without any precedent merits of good works, was joined to God the Word in the womb of the Virgin, so that with it it became one person. Therefore it is that we confess Him to have been born of the Holy Spirit and of the Virgin Mary. For it is most absurd to believe Him to have received the Holy Spirit when He was near thirty years old: for at that age He was baptized by John; but that He came to baptism as without any sin at all, so not without the Holy Spirit. For if it was written of His servant and forerunner John himself, “He shall be filled with the Holy Spirit, even from his mother's womb,” because, although generated by his father, yet he received the Holy Spirit when formed in the womb; what must be understood and believed of the man Christ, of whose flesh the very conception was not carnal, but spiritual? Both natures, too, as well the human as the divine, are shown in that also that is written of Him, that He received of the Father the promise of the Holy Spirit, and shed forth the Holy Spirit: seeing that He received as man, and shed forth as God. And we indeed can receive that gift according to our small measure, but assuredly we cannot shed it forth upon others; but, that this may be done, we invoke over them God, by whom this is accomplished.
Source: On the Holy Trinity (New Advent)