Being about to prove that the will, the calling, and the commandment of the Trinity is one, St. Ambrose shows that the Spirit called the Church exactly as the Father and the Son did, and proves this by the selection of SS. Paul and Barnabas, and especially by the mission of St. Peter to Cornelius. And by the way he points out how in the Apostle's vision the calling of the Gentiles was shadowed forth, who having been before like wild beasts, now by the operation of the Spirit lay aside that wildness. Then having quoted other passages in support of this view, he shows that in the case of Jeremiah cast into a pit by Jews, and rescued by Abdemelech, is a type of the slighting of the Holy Spirit by the Jews, and of His being honoured by the Gentiles.
101. And not only is the operation of the Father, Son, and Holy Spirit everywhere one but also there is one and the same will, calling, and giving of commands, which one may see in the great and saving mystery of the Church. For as the Father called the Gentiles to the Church, saying: “I will call her My people which was not My people, and her beloved who was not beloved;” and elsewhere: “My house shall be called a house of prayer for all nations,” so, too, the Lord Jesus said that Paul was chosen by Him to call forth and gather together the Church, as you find it said by the Lord Jesus to Ananias: “Go, for he is a chosen vessel unto Me to bear My name before all nations.”
102. As, then, God the Father called the Church, so, too, Christ called it, and so, too, the Spirit called it, saying: “Separate Me Paul and Barnabas for the work to which I have called them.” “So,” it is added, “having fasted and prayed, they laid hands on them and sent them forth. And they, being sent forth by the Holy Spirit, went down to Seleucia.” So Paul received the apostleship by the will not only of Christ, but also of the Holy Spirit, and hastened to gather together the Gentiles.
103. And not only Paul, but also, as we read in the Acts of the Apostles, Peter. For when he had seen in his prayer heaven opened and a certain vessel tied at the four corners, as it were a sheet in which were all kinds of four-footed beasts and wild beasts and fowls of the air, “a voice came to him saying, Arise, Peter, kill and eat. And Peter said, Be it far from me, Lord, I have never eaten anything common or unclean. And again a voice came to him, saying, What God has cleansed, call not common. And this was done three times, and the vessel was received back into heaven.” And so when Peter was silently thinking over this with himself, and the servants of Cornelius appointed by the Angel had come to him, the Spirit said to him, “Lo, men are seeking you, rise therefore, and go down and go with them; doubt not, for I have sent you.”
104. How clearly did the Holy Spirit express His own power! First of all in that He inspired him who was praying, and was present to him who was entreating; then when Peter, being called, answered, “Lord,” and so was found worthy of a second message, because he acknowledged the Lord. But the Scripture declares Who that Lord was, for He Whom he had answered spoke to him when he answered. And the following words show the Spirit clearly revealed, for He Who formed the mystery made known the mystery.
105. Notice, also, that the appearance of the mystery three times repeated expressed the operation of the Trinity. And so in the mysteries the threefold question is put, and the threefold answer made, and no one can be cleansed but by a threefold confession. For which reason, also, Peter in the Gospel is asked three times whether he loves the Lord, that by the threefold answer the bonds of the guilt he had contracted by denying the Lord might be loosed.
106. Then, again, because the Angel is sent to Cornelius, the Holy Spirit speaks to Peter: “For the eyes of the Lord are over the faithful of the earth.” Nor is it without a purpose that when He had said before, “What God has cleansed call not thou common,” the Holy Spirit came upon the Gentiles to purify them, when it is manifest that the operation of the Spirit is a divine operation. But Peter, when sent by the Spirit, did not wait for the command of God the Father, but acknowledged that that message was from the Spirit Himself, and the grace that of the Spirit Himself, when he said: “If, then, God has granted them the same grace as to us, who was I that I should resist God?”
107. It is, then, the Holy Spirit Who has delivered us from that Gentile impurity. For in those kinds of four-footed creatures and wild beasts and birds there was a figure of the condition of man, which appears clothed with the bestial ferocity of wild beasts unless it grows gentle by the sanctification of the Spirit. Excellent, then, is that grace which changes the rage of beasts into the simplicity of the Spirit: “For we also were aforetime foolish, unbelieving, erring, serving various lusts and pleasures. But now by the renewing of the Spirit we begin to be heirs of Christ, and joint-heirs with the Angels.”
108. Therefore the holy prophet David, seeing in the Spirit that we should from wild beasts become like the dwellers in heaven, says, “Rebuke the wild beasts of the wood,” evidently signifying, not the wood disturbed by the running of wild beasts, and shaken with the roaring of animals, but that wood of which it is written: “We found it in the fields of the wood.” In which, as the prophet said: “The righteous shall flourish as the palm-tree, and shall be multiplied as the cedar which is in Libanus.” That wood which, shaken in the tops of the trees spoken of in prophecy, shed forth the nourishment of the heavenly Word. That wood into which Paul entered indeed as a ravening wolf, but went forth as a shepherd, for “their sound is gone out into all the earth.”
109. We then were wild beasts, and therefore the Lord said: “Beware of false prophets, which come in sheep's clothing, but inwardly are ravening wolves.” But now, through the Holy Spirit, the rage of lions, the spots of leopards, the craft of foxes, the rapacity of wolves, have passed away from our feelings; great, then, is the grace which has changed earth to heaven, that the conversation of us, who once were wandering as wild beasts in the woods, might be in heaven.
110. And not only in this place, but also elsewhere in the same book, the Apostle Peter declared that the Church was built by the Holy Spirit. For you read that he said: “God, Which knows the hearts of men, bore witness, giving them the Holy Spirit, even as also to us; and He made no distinction between us and them, purifying their hearts by faith.” In which is to be considered, that as Christ is the Cornerstone, Who joined together both peoples into one, so, too, the Holy Spirit made no distinction between the hearts of each people, but united them.
111. Do not, then, like a Jew, despise the Son, Whom the prophets foretold; for you would despise also the Holy Spirit, you would despise Isaiah, you would despise Jeremiah, whom he who was chosen of the Lord raised with rags and cords from the pit of that Jewish abode. For the people of the Jews, despising the word of prophecy, had cast him into the pit. Nor was there found any one of the Jews to draw the prophet out, but one Ethiopian Abdemelech, as the Scripture testifies.
112. In which account is a very beautiful figure, that is to say, that we, sinners of the Gentiles, black beforehand through our transgressions, and aforetime fruitless, raised from the depth the word of prophecy which the Jews had thrust down, as it were, into the mire of their mind and carnality. And therefore it is written: “Ethiopia shall stretch out her hand unto God.” In which is signified the appearance of holy Church, who says in the Song of Songs: “I am black and comely, O daughters of Jerusalem;” black through sin, comely through grace; black by natural condition, comely through redemption, or certainly, black with the dust of her labours. So she is black while fighting, is comely when she is crowned with the ornaments of victory.
Source: On the Holy Spirit (New Advent)