Bede : Because the Holy Spirit well spoke through Isaiah the prophet to your fathers, saying: "Go to this people and say: You will hear indeed, etc." This prophecy, which the Apostle affirms was pronounced by the Holy Spirit, the book of the prophet itself recalls as having been spoken by the Lord. From this, it is clearly shown that the will and nature of the Lord and the Holy Spirit are one, and the name of the Lord is also understood in the appellation of the Spirit. And indeed, Paul, having no other Holy Spirit when he wrote these things about him, who was in the prophets before the coming of the Lord, was referring to the same Spirit of whom he himself was also a partaker, and all those who were brought in the faith of perfect virtue. Hence, he mentions the Spirit with the article, confirming it to be singular and one, and as he says, not simply "Holy Spirit," but with the added article "the Holy Spirit," and he recalls Isaiah prophesying with the word "the Holy Spirit." Peter too, in that speech by which he persuaded the present, said: "It was necessary for the Scripture to be fulfilled which the Holy Spirit spoke (that is, 'the Holy Spirit') through the mouth of David concerning Judas" (Acts I). He too shows that the same Spirit worked in the prophets and in the apostles. These excerpts from the books of the blessed Didymus should hold this place in our writings. — Commentary on Acts Hippolytus of Rome : This is the Spirit that at the beginning "moved upon the thee of the waters; " by whom the world moves; by whom creation consists, and all things have life; who also wrought mightily in the prophets, and descended in flight upon Christ. This is the Spirit that was given to the apostles in the form of fiery tongues. This is the Spirit that David sought when he said, "Create in me a clean heart, O God, and renew a right spirit within me." Of this Spirit Gabriel also spoke to the Virgin, "The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee." By this Spirit Peter spake that blessed word, "Thou art the Christ, the Son of the living God." By this Spirit the rock of the Church was stablished. This is the Spirit, the Comforter, that is sent because of thee, that He may show thee to be the Son of God. — Fragments - Dogmatic and Historical John Chrysostom : "And when they agreed not among themselves, they departed, after that Paul had spoken one word, Well spake the Holy Ghost by Esaias the prophet unto our fathers, saying, Go unto this people, and say, Hearing ye shall hear, and shall not understand; and seeing ye shall see, and not perceive: for the heart of this people is waxed gross, and their ears are dull of hearing, and their eyes have they closed; lest they should see with their eyes, and hear with their ears, and understand with their heart, and should be converted, and I should heal them." But when they departed, as they were opposed to each other, then he reproaches them, not because he wished to reproach those that believed not, but to confirm these that believed. "Well said Esaias," says he to them. So that to the Gentiles it is given to know this mystery. No wonder then, if they did gainsay: this was foretold from the first. — Homily on Acts 55 John Chrysostom : "Well said the Spirit:" as much as to say, It is not me that ye disbelieve. But God foreknew this from the first. "He discoursed," it says, "with boldness, unhindered": for it is possible to speak with boldness, yet hindered. His boldness nothing checked: but in fact he also spoke unhindered. — Homily on Acts 55 John Chrysostom : "Well spake the Holy Ghost," etc. But this saying, "The Spirit said," is nothing wonderful: for an angel also is said to say what the Lord saith: but He the Spirit not so. When one is speaking of the things said by the angel, one does not say, Well said the angel, but, Well said the Lord. "Well said the Spirit:" as much as to say, It is not me that ye disbelieve. But God foreknew this from the first. — Homily on Acts 55 Oecumenius : To those who call him the minister of the Father, Paul here gives a severe rebuke concerning the Holy Spirit. For concerning the Lord seated on a high and exalted throne, whom Isaiah saw, therefore speaks the Holy Spirit. For He is of the same essence as the Father and the Son, and shares the same power. And this utterance prepares the prophet's words as if voiced by God concerning those things which pertain to Jesus, since the people heard the words of Jesus and did not understand, and seeing the wondrous works done by him did not see. — Commentary on Acts