We often urge people to be converted by believing in Jesus’ resurrection with their heart and confessing with their mouth that Jesus is Lord. This summary of how to respond to the gospel is based on Romans 10:9-10, which does in fact discuss salvation. But it is helpful to examine why Paul specifically mentions the mouth and heart here (rather than in some other passages which emphasize different aspects of salvation). Certainly Paul would not deny that a deaf mute could be saved simply because they could not confess with their mouth. He chooses the particular words “heart” and “mouth” for specific reasons evident in the context.
We look first at the immediate context. Paul believes that we are saved by God’s grace, not by our works. Contrary to the means of justification proposed by Paul’s opponents (Rom. 10:1-5), Paul demonstrates from the law of Moses itself that the message of faith is the saving word (10:6-7). As Moses said, “the word is near you, in your mouth and in your heart” (10:8); Moses was referring to the law (Deut 30:10-11, 14), but the principle was also applicable to the gospel, which was also God’s word. In Moses’ day one could not ascend to heaven to bring the law down from above; God in his mercy already gave it to Israel on Mount Sinai (30:12). Nor was it necessary to descend again into the sea (30:13); God had already redeemed his people and brought them through the sea. They could not save themselves; they had to depend on God’s mighty grace (cf. Ex 20:2). In the same way, Paul says, we don’t bring Christ up from the dead, or send him down from the Father; like the law and Israel’s redemption, Christ’s salvation is God’s gift to us (Rom 10:6-7). Moses declared that this message was “in your mouth and in your heart” (Deut 30:14), i.e., already given to Israel by God’s grace. Paul explains that likewise God’s message was in your mouth when you confessed Christ with your mouth and in your heart when you believed in Him in your heart (Rom 10:9-10). Faith could come only from hearing this word, the gospel of Christ (10:17), as we noted above.
The immediate context explains why Paul mentions the “mouth” and the “heart” in this specific passage, but it also raises a new question. Why did Paul have to make an argument from the Old Testament that salvation was by grace through faith? Was there anyone who doubted this? Reading Romans as an entire book explains the reason for each passage within that book. Paul is addressing a controversy between Jewish and Gentile Christians.
Paul begins Romans by emphasizing that the Gentiles are lost (Rom 1:18-32); just as the Jewish Christian readers are applauding, Paul points out that religious people are also lost (Rom 2), and summarizes that everyone is lost (Rom 3). Paul establishes that all humanity is equally lost to remind us that all of us have to come to God on the same terms; none of us can boast against others.
But most Jewish people believed that they were chosen for salvation in Abraham; therefore Paul reminds his fellow Jewish Christians that it is spiritual rather than ethnic descent from Abraham that matters for salvation (Rom 4). Lest any of his Jewish readers continue to stress their genetic descent, he reminds them that all people–including themselves–descend from sinful Adam (5:12-21). Jewish people believed that most Jews kept all 613 commandments in the law (at least most of the time), whereas most Gentiles did not even keep the seven commandments many Jews believed God gave to Noah. So Paul argues that while the law is good, it never saved its practitioners, including Paul (Rom 7); only Jesus Christ could do that! And lest the Jewish Christians continue to insist on their chosenness in Abraham, Paul reminds them that not all Abraham’s physical descendants were chosen, even in the first two generations (Rom 9:6-13). God was so sovereign, he was not bound to choosing people on the basis of their ethnicity (9:18-24); he could choose people on the basis of their faith in Christ.
But lest the Gentile Christians look down on the Jewish Christians, Paul also reminds them that the heritage into which they had been grafted was, after all, Israel’s (Rom 11). God had a Jewish remnant, and would one day turn the majority of Jewish people to faith in Christ (11:25-26). And at this point Paul gets very practical. Christians must serve one another (Rom 12); the heart of God’s law is actually loving one another (13:8-10). Ancient literature shows that Roman Gentiles made fun of Roman Jews especially for their food laws and holy days; Paul argues that we should not look down on one another because of such minor differences of practice (Rom 14). He then provides examples of ethnic reconciliation: Jesus though Jewish ministered to the Gentiles (15:7-12) and Paul was bringing an offering from Gentile churches for the Jewish Christians in Jerusalem (15:25-31). In the midst of his closing greetings, he offers one final exhortation: Beware of those who cause division (16:17).
Getting the whole picture of Romans provides us a clearer understanding of the function of each particular passage in the work as a whole. It also suggests the sort of situation which the letter addresses. What we know of the “background” sheds more light on this situation: Rome earlier expelled the Jewish Christians (Acts 18:1-3), but now they have returned (Rom 16:3). This means that the Roman house churches, which had consisted completely of Gentiles for many years, now face conflict with Jewish Christians who had different cultural ways of doing things. Paul’s letter to the Romans summons Christians to ethnic, cultural, tribal reconciliation with one another by reminding us that all of us came to God on the same terms, through Jesus Christ alone.