In these first seven verses, Paul introduces himself and his mission. Paul says he is a slave of Christ Jesus, set apart for apostleship, given a mission to call others to obedience in faith, to be saints and to belong to Jesus.
We don't have a great modern understanding of the relationship Paul claims to have with Jesus. It is stronger than an employee and more voluntary than purchased slavery. The best way to express it is really that Paul has sold out to Christ. Jesus actually owns him and directs his life.
Paul says he has been set apart for a purpose. William Barclay suggests that this is a play on words, as Pharisee can be interpreted as Set-apart-one. Paul had been a Pharisee, set apart for his own personal holiness. Now Paul is set apart for a purpose, for the benefit of others.
Paul's purpose is to be sent out among the nations. The book of Acts gives us this picture of Paul constantly going out, moving on, and moving further into territory where people have never heard. He went out to call people to obedience that comes from faith.
Obedience from faith is much different than obedience from obligation or fear of punishment. We have all experienced obedience that does not come from faith. We all had parents who told us to obey "Because I said so!" We all had teachers and employers who required obedience on pain of detention, docking our wages or firing. Paul's mission is to call people to obedience that comes from faith that God is good.
Many of us grew up seeing God as someone to be afraid of a cosmic punisher of wrong. It is not that God does not represent judgment, but rather that he is not sitting somewhere waiting for us to mess up so that he can hurl lightning at us. When we come to know and understand who God is, his kindness, mercy and compassion, we obey from faith in who he is and from our love for him.
Paul also calls these people at Rome to belong to Jesus. Paul has introduced himself as one who is sold out to Christ, and he is calling those reading this letter to do the same. When we believe in Christ Jesus as Lord, we must in that recognition give him our very selves. If he is to be Lord, he must be our Lord. He must own our lives.
Finally, Paul calls these believers saints. Most of us would not raise our hands if a call were made for saints. We see sainthood as a state of perfection, and it does mean "Holy one." Holy is a tricky word that at its core means "set apart." Paul is calling people to be as he is, set apart for God's purpose.
In essence, Paul is saying in this introduction "This is who I am, and I am calling you to the same life, purpose and Lord." That was his challenge to the Romans, and it is my challenge to you. You have been called to obedience that comes from faith, to belong to Jesus at the core of your being, so that you will be set apart for his purpose.