"The fathers received the promise, but you have received the deed itself." According to Saint John Chrysostom, the apostle was, as it were, speaking to them in this way.
"The eyewitnesses had proofs of the truth of Christ's Resurrection that were, so to speak, factual, for they had seen Him. Paul and Barnabas, in their preaching, give a theoretical proof from Scripture.
The promises of God are immutable, and God fulfilled them by raising Jesus. By the promises here are meant, in general, the Old Testament promises of God concerning the Messiah, the Savior of the world.
If Christ had not risen, these promises would not have been fulfilled. For, had He not risen, He would not be Christ, the Savior of the world.
The apostle points to one of these promises of God in the words of Psalm 2: "You are My Son" (Ps 2:7).
The apostle first proves the truth of the Resurrection of Jesus Christ by referring to eyewitnesses. Through the appearance of the Risen One to them over a considerable period, they were convinced by experience of the reality of this event.
The apostle does not number himself among these immediate eyewitnesses of the Risen Lord. He saw the Lord (see Acts 9:3; 1 Cor 15:8), but under wholly different circumstances.
He beheld Christ in His heavenly, divine majesty and glory. As the God-man, Christ entered into possession of these after His Ascension into heaven (see Acts 19:41).
Nevertheless, Paul considers it possible to number himself, together with Barnabas, among the proclaimers of the Resurrection. "And we preach good tidings to you."
In this preaching of Christ's Resurrection, the apostle points to its trustworthiness. God has finally fulfilled the promise, or all the promises, concerning the Savior, which are immutable and so revered by the Jews.
He has fulfilled them only now, for their children (cf. 1 Pet 1:12), through the Resurrection of Jesus.
The Resurrection is the fulfillment of all the promises concerning the Kingdom of the Messiah.
"That the Resurrection has precisely this meaning, that in it the Messiah first appeared, so to speak, as Messiah, the apostle proves in the more intelligible language of Old Testament prophecies."