According to the explanation of Saint John Chrysostom, the Apostles spoke to the Jews as if saying: "The Gentiles must hear the word of God. Yet it depends not on us, but on you, that they will have to hear it before you. The teaching of the Lord had to be preached first to you (see Acts 1:8; 3:26; Rom 1:16). But since you refuse to hear us, then, in fulfillment of another decree of God spoken about the Messiah through the prophet Isaiah, we shall enlighten the Gentiles and order salvation for them to the ends of the earth."
And again a blow was dealt to envy. The Jews did not wish to see the conversion of their fellow citizens. Yet they had to hear that the conversion of people throughout the whole world to Christ was being prepared.
"Do you see," says Saint John Chrysostom, "how, because of the Jews' resistance, they extended their preaching farther and turned still more to the Gentiles, having justified themselves and made themselves free from accusations before their own kinsmen?"
"We turn to the Gentiles." He does not say, "We leave you," but speaks in such a way as to allow the possibility of his return to Antioch.
The expression "with boldness" is worthy of note. This boldness is mentioned because, although Jesus Christ Himself commanded them to preach to the whole world (see Mt 28:19), this was not yet a universally recognized matter.
For this reason, there were various perplexities concerning preaching among the Gentiles (see Acts 11:2-3, 15). At the same time, it must be said that Paul and Barnabas were not unaware of cases of the Gentiles' conversion (see Acts 10; Acts 11:20).
Therefore their boldness was, so to speak, firm and resolute.
The malicious attitude of the Jews toward the word of salvation gives the Apostles occasion to declare boldly, with confidence, as is proper to true ministers of the Word (see Prov 1:21), that they now turn with this word of salvation to the Gentiles.
They declare that they are now Apostles of the Gentiles (see Rom 11:13). In justifying this declaration, the Apostle Paul here expresses the same thoughts about the Jews and their relation to salvation that later received full development in the Epistle to the Romans (see Rom 10:19-21).
"According to the divine decree concerning the salvation of the human race, you were the first who had to hear the word of God and receive salvation (verse 26), so as to spread it to the ends of the earth. But since you reject this word of life (see Acts 5:20), and by this make yourselves unworthy of eternal life, whose bestowal is the purpose of the Messiah's coming, behold, we turn to the Gentiles. For from eternity God appointed the Messiah to be a light for the Gentiles and salvation to the end of the earth. As proof of this thought, the Apostle cites the words from the book of the prophet Isaiah (49:6). These words also serve the Apostles as a commandment to preach among the Gentiles, because the words of God would not have been fulfilled if their preaching had not taken place."