Romans stands apart from Paul's other letters in one basic fact: he did not found the church he is writing to, had never visited it, and wrote instead to introduce himself before an intended trip. The result is his most systematic letter, closer to a theological treatise than to the occasional, dispute driven correspondence of Corinthians or Galatians. Its argument opens from universal human failure, "all have sinned and fall short of the glory of God," before turning to its central claim, righteousness before God comes through faith rather than through observance of the law, anchored in the quotation from Habakkuk, "the righteous shall live by faith," which later became the rallying text of the Protestant Reformation. Chapters 9 through 11 turn to a harder question the letter cannot avoid: what becomes of Israel, God's first chosen people, if righteousness now comes by faith rather than by the law given to Moses.
Paul's answer, that Israel's partial hardening is temporary and that "all Israel will be saved," has generated centuries of interpretive disagreement and sits at the center of modern Jewish Christian dialogue. The letter closes with sixteen chapters' worth of practical instruction, on civil authority, on love as the fulfillment of the law, and a long list of personal greetings naming more individuals, many of them women, than any other Pauline letter.