John Chrysostom
Therefore they spoke to you, and everything was for you. Since, because of their crime, they considered themselves estranged, the Apostle shows that both this and that agree with prophecy.
It was not natural to think that the One whom they crucified would care for them as His own. "You," he says, "are sons," that is, heirs of the covenant.
Lest they think they receive this by Peter's favor, he shows that it was to belong to them from of old. Thus they would more readily believe that this is pleasing to God.
What does "sons of the prophets and of the covenant" mean? It means heirs, successors. Therefore, if you are sons, why do you treat what is yours as though it were foreign?
Certainly you have done what deserves condemnation. Yet despite this, you can receive forgiveness.