John Chrysostom

"To Him give all the prophets witness, that through His name, whosoever believeth in Him shall receive remission of sins." This is a proof of that which was about to be: this is the reason why he here cites the Prophets. "To him give all the Prophets witness," etc. When by the terror he has agitated them, then he brings in the pardon, not spoken from himself but from the Prophets. And what is terrifying is from him, what is mild from the Prophets.

Homily on Acts 23 ↗

Theophylact of Ohrid

"All the prophets bear witness about Him." Whatever prophets spoke about the remission of sins, they all said that sins are forgiven in this Jesus. Thus Isaiah also speaks in His person: "I, even I, am He who blots out your transgressions for My own sake, and I will not remember your sins" (Isa. 43:25). Peter, however, did not say that He is the Son of God, but rather what frightened them more — the preparation suited to the occasion is drawn from the prophets, because they enjoyed great renown. …

Commentary on Acts ↗

Oecumenius

Those who, he says, prophesied spoke concerning the forgiveness of sins; in this matter they said that these are forgiven by Jesus. Therefore also Isaiah, bringing forward his very person, says: "I am the one who wipes away your sins, and your lawless deeds." (Isa. 43:25)

Commentary on Acts ↗