John Chrysostom

Great boldness of speech! And the ground of their credibility: "And so is also the Holy Ghost, Whom God hath given to them that obey Him." Do you observe that they allege not only the Spirit's testimony? And they said not, "Whom He hath given" to us, but, "to them that obey Him:" therein alike showing their own unassuming temper, and intimating the greatness of the gift, and showing the hearers that it was possible for them also to receive the Spirit. …

Homily on Acts 13 ↗

Theophylact of Ohrid

They did not say, "the Holy Spirit, whom God has given to us," but "whom God has given to those who obey Him," at once both showing humility and revealing great truths, and besides that, also declaring that the Jews themselves could have received the Spirit, because it was precisely for this reason that God allowed the apostles to be led into the court — so that the Jews too might be instructed, and the apostles themselves might gain greater boldness, and all in general might receive edification.

Commentary on Acts ↗

Oecumenius

That there was mercy, because he promised repentance. For the resurrection was therefore already confessed.

Commentary on Acts ↗

Bede

And we are witnesses of these words, and the Holy Spirit whom God gave to all who obey Him. We are witnesses because we have seen the glory of His resurrection, because we have followed with our eyes as He ascended into the heavens. The Holy Spirit is also a witness, because as we proclaim to you the great works of God with unyielding proclamation, He has strengthened us with His presence, He has formed these words in us as He speaks within us. …

Retractions on Acts ↗