Paul's letter to the church in Rome - where he had not yet visited - is best understood as Paul writing the things he would otherwise have spoken had he been able to schedule a visit there. Paul wants Jewish and Gentile believers to understand the gospel in such a way that they can live together peaceably in one church. The level of writing is on a pastoral level, not on an academic or professional level, it is the sort of thing a pastor might say in a small Bible study group.