Romans: Greeting (1:1-2)
Paul, a servant of Christ Jesus, called to be an apostle, set apart for the gospel of God, 2 which he promised beforehand through his prophets in the holy Scriptures,
It's common to suggest that the Lord changed Saul's name to Paul at his conversion on the Road to Damascus (Acts 9:1-19). This is a popular misconception. While our Lord did change the name of some disciples throughout redemptive history (Abram to Abraham, Sarai to Sarah, and Jacob to Israel, etc.), this was never the case with Paul. The name Paul is simply the Roman variant of the Hebrew name, Saul. It's assuredly for this reason that, when writing the Roman Christians, he wisely employed the version of his name most familiar to them.
Never having visited the church at Rome, Paul continued by carefully describing himself as both a servant and apostle. The former (literally, slave) emphasized Paul's shared and humble position as a fellow disciple, something that no doubt endeared him to the church, even and perhaps especially those of its lowest social strata. The latter emphasized his unique and high calling as a Christ-appointed leader of the Christian movement with authority, despite having never met them personally, over the Roman Christians. No doubt, these twin designations served Paul well as he sought to establish some sense of intimacy, credibility, and ultimately authority among his Roman audience ahead of his planned visit and appeals for their support.
We do well to remember that the word "gospel" (good news) was not unique to the Christian movement, but rather quite common at the time of Paul's writing - and perhaps especially among those living in the imperial center of Rome. So-called gospel proclamations routinely accompanied the announcements of military victory, the accession of a new emperor, and so on. It's for this reason that Paul specifies his gospel as the ultimate good news, the "gospel of God."
Paul then emphasized his gospel as the outworking of God's plan promised initially through the prophets of the Old Testament, writings he highlighted as holy Scripture. In so doing, Paul invited his readers to recognize both the fidelity of his teaching to Scripture, but also his ministry as a divinely-appointed complement to (and continuation of) the ministries of Old Testament prophets.