No New Testament book has shaped Western Christian doctrine as decisively as Romans. Augustine traced his own conversion to a chance reading of Romans 13; a millennium later, Martin Luther's reading of Romans 1:17, "the righteous shall live by faith," became the seed of the doctrine of justification by faith alone that split Western Christianity at the Reformation, and John Wesley later described his own evangelical awakening as his heart being "strangely warmed" while a preface to Romans was being read aloud.
Catholic and Orthodox tradition draw on the same letter differently, reading its emphasis on faith alongside its equal insistence, a few chapters later, on transformed conduct, "be transformed by the renewing of your mind," and resisting any reading that separates faith entirely from the sacraments and moral life the other traditions also root in Paul's wider letters.
Romans 9 through 11, on Israel's ongoing place in God's purposes, has taken on new theological weight since the mid 20th century, cited on all sides of Christian reckoning with the history of Christian anti-Judaism and used by many mainline churches to reject any theology that treats the church as having simply replaced Israel. The letter's density has also made it the New Testament book most quoted, verse for verse, in later systematic theology, Catholic, Orthodox and Protestant alike.