that if you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised Him from the dead, you will be saved.
Paul is writing to a mixed church of Jewish and non-Jewish believers in Rome, and he's grieving that many of his own people haven't accepted Jesus. Here he borrows words from Moses to say the message isn't far off or hard to reach. In that world, "Lord" was also what people called Caesar.
Romans, chapter 10. A letter from Paul to the church in Rome, setting out how people are made right with God.