This is the start of Romans, one of Paul's many letters he wrote to various churches in his ministry. In the introduction, and Paul introduces himself as "a bondservant of Jesus Christ" who is "called to be an apostle" and "separated to the gospel of God" (1:1). In other words, Paul is one of the first major church leaders -- and he takes his Jesus calling seriously!
But not only that, Paul also provides a description about Jesus himself (as well as the gospel).
The gospel is announced beforehand via past prophets (1:2). Isaiah is a major example of a prophet who proclaimed the promise of a Savior now known as Jesus before the event happened.
The gospel is about Lord Jesus, who is a descendant of King David and born "according to flesh" (1:3). Basically, Jesus was a human.
Jesus was declared Son of God with power from Holy Spirit, as seen from the resurrection feat (1:4).
As you'll see, Jesus is a very important person discussed throughout Romans. No wonder Paul outlines who Jesus is (even more than who Paul is) in the introduction.