Paul, writing in the previous verse, quoted Isaiah 52:7 and seemingly applied it to himself and the other apostles commissioned by Jesus to preach the gospel of faith in Christ to the world. That verse says, “How beautiful are the feet of those who preach the good news!”
Now Paul seems to say that everything needed has been given to Israel to bring them to salvation. Each required step from the previous two verses has been fulfilled. Christ sent preachers. The apostles preached. The Jewish people heard. The problem, Paul now insists, is that the Jewish people did not believe. More specifically, Paul writes that they did not “obey” the gospel.
For Paul, failure to believe in Christ amounts to more than just an inability to accept the truth of the gospel. Paul calls it disobedience, a stubborn refusal to receive the Messiah and believe in Jesus. This is consistent with the Bible’s general teaching, which is that a person’s willingness to believe—or not—is always more influential than knowledge or arguments (John 5:39–40; 7:17).
This time, Paul quotes from Isaiah 53:1 to support his case to his Jewish readers. In that verse, the prophet asks the Lord, “Who has believed what he has heard from us?” Paul is showing that Israel’s tendency to disobey, specifically by refusing to believe, goes all the way back to the days of the prophets.
Paul’s heart is broken for his people, Israel. He prays they will be saved through faith in Christ. Their enthusiasm for God is made useless by their attempt to be made righteous by their own law-keeping instead of by faith in Christ. What, then, is required to be saved? One must confess that Jesus is Lord and believe that God raised Him from the dead. The same is true for both Jews and Gentiles. God waits patiently for Israel to turn and believe.
Romans 10:14–21 explains that, despite hearing the gospel and understanding it, Israel continues to disobey. Paul works through a series of questions, showing where and how Israel has failed to accept the truth given them by God. His point is clear: the people of Israel have been given more than enough knowledge, and so they ought to recognize their Messiah. Despite that stubbornness and failure, God waits, still holding out His hands to His people.