Romans 10:7-10 says, 'Or, ''Who will descend into the abyss?'' (that is, to bring Christ up from the dead).8 But what does it say? 'The word is near you, in your mouth and in your heart' (that is, the word of faith which we preach): that if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation.'
First of all, we know that these words were written to people who were already saved (Romans 1:7). They had already repented and been baptized in the name of Jesus Christ (Romans 6:1-3). They had already been set free from sin (Romans 6:17-18). We can therefore conclude that Paul was not telling the Romans how to come to God and receive salvation. They had already done that by obeying the plan Peter announced in Acts 2:38.
The real purpose of these verses was to admonish people who had already obeyed the gospel to “get out of the closet” so to speak. That is, Paul was encouraging them not to be ashamed of the gospel, but to speak out and testify--to confess Christ publically. Paul got on this subject of being “ashamed” early in his letter to the Romans (“for I am not ashamed...” 1:16). The word “ashamed” is used four more times in Romans, the last time in Chapter 10, right in the middle of these famous comments about “public confession.” It is then never mentioned again in this letter. Why would there be five references to being ashamed of the gospel in the first ten chapters, but none in the remaining six? Because, after his comments about public confession of Christ, the subject had been exhausted, and Paul, having made his point, moved on.
The purpose of his comments about making a public confession of faith was not to establish the plan of salvation to people who were already saved; it was to exhort and admonish those who were Christians to be public about their faith and to not be ashamed. One of the important themes of the book Romans is set forth in Romans 1:16 and driven home hard in Romans 10:7-10.