1:1 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, 3 concerning his Son, who was descended from David  according to the flesh 4 and was declared to be the Son of God in power according to the Spirit of holiness by his resurrection from the dead, Jesus Christ our Lord, 5 through whom we have received grace and apostleship to bring about the obedience of faith for the sake of his name among all the nations, 6 including you who are called to belong to Jesus Christ,7 To all those in Rome who are loved by God and called to be saints: Grace to you and peace from God our Father and the Lord Jesus Christ. (Romans 1:1-7 (ESV)
“You who are called to belong to Jesus Christ… loved by God and called to be saints.”
Paul writes his opus magnum to the Romans. It is perhaps his most important book. The entire Pauline Corpus is categorized by size starting with the longest book, Romans and ending with Philemon which would have covered two sheets of papyrus in a scroll. Yet it is good that Romans maintains priority ahead of the rest of the letters, in many ways it provides the key to understanding the rest of his letters, and is the most important of them all.
The Pauline Corpus was largely written in reaction to controversy. This is not true of Romans. Often when reading Paul’s letters to Corinthians or to the Ephesians it is necessary to read between the lines and behind the text to piece together the situation he is addressing, and only then can you really get an accurate understanding of what he means by what he writes. But in Romans Paul writes to people who he doesn’t know. He isn’t writing to any particular situation of which he has any personal familiarity. This gives him occasion to lay out Christian doctrine and his theology in as straightforward a manner as possible. So a thorough understanding of Paul’s letter to Romans becomes a great asset to understanding the resto of Paul’s letters. This is the sort of hermeneutical perspective that is behind the reformation contention that scripture interprets scripture. Sure there are areas that on their own can be hard to understand, and twisted to mean things that are at odds with Christian doctrine as a whole, but when illuminated by clear scripture they too become clear, or at least can no longer be used to put forth unchristian doctrine. It is for this reason that Romans has always been a favorite for Lutherans.
Paul writes to the Romans who he says are called to belong to Christ and called to be saints. The phrase to be can be read in a couple different ways. In one way it could be that they do not yet belong to Christ and are not yet saints. In this sort of reading Romans becomes a road map to heaven, rather than a proclamation of the gospel. But in a practical exercise in Scripture interpreting scripture we read that Paul is called to be an apostle. And here we find a key to the proper understanding of this phrase. Paul is called to be and so he is. It is a present reality for him. It is also a present reality for the Romans that he is writing to that they are what they are called to be, saints. Those who are called to belong to Christ belong to Christ who is God of God and King of kings. It is an inescapable reality. It is this for you too.