By the time Paul wrote his epistle to the church at Rome in the late 50s AD, it was clear that vast numbers of Jews had refused to believe Jesus of Nazareth was their Messiah. This led the early Christian community to search for the reasons why, since Jewish Apostles were proclaiming Jesus as the fulfillment of the oracles given to the people of Israel (Rom. 1:1-7; 4:1-12; 9:1-5). Paul considers the answer from two perspectives. First, from a heavenly point of view, the failure of many Jews to believe was a consequence of divine election—not every Jew according to the flesh was chosen by the Lord for salvation (9:6-28). God's election unto salvation, however, also incorporates and establishes human decisions, so from a human perspective, many Jews did not believe because they missed the point of the Mosaic law. Instead of seeing the reflection of their own sin in it, they sought to establish their own righteousness by their works, and they stumbled over Christ. They missed the simple message that God saves His people by grace alone from first to last, and they did not receive the gospel message even though it was close at hand (9:29-10:13).
In today's passage, Paul begins to argue that the Jews who did not believe in Christ could not plead ignorance as an excuse. He makes that argument specifically in Romans 10:18, but he leads up to that by noting the requirement of Christian preaching if people are to be saved. Having noted that all who call upon the name of the Lord will be saved (v. 13; see Joel 2:32), Paul asks a series of questions related to one's ability to call upon the name of the Creator for salvation. His essential point in Romans 10:14-15 is that no one can call upon the name of a person whom they do not know, and so the good news of Christ Jesus must be taken to the ends of the earth so that people can have the opportunity to believe in Him. Our preaching of the gospel will not guarantee the right response—that is God's job, which He accomplishes through His Holy Spirit in the act of regeneration (John 3:1-8). Nevertheless, the preaching of the Word of God and its fulfillment in Christ Jesus is the Lord's ordinary means of bringing His truth to people so that His Spirit can work to convert the elect. Preachers, moreover, cannot go unless the church sends them, commissioning them for ministry and supporting their physical needs (Rom. 10:14-15). The task of reaching the nations is not accomplished by solo missionaries who strike out on their own. Instead, the church trains and sends forth sound preachers of the gospel.
Dr. R.C. Sproul writes in his commentary Romans that "not everyone in the church is called to be a missionary, but every member of the church is responsible to make sure that the missionary activity gets done." The Great Commission is not for a select few; rather, it is given to the whole church. Some of us will go to the ends of the earth. Some of us will send out missionaries, supporting them financially and in prayer. But all of us must take part in this great work.