Which of St. Paul’s thirteen epistles has “pride of place”?

Romans comes first because it is the longest and also the most important for two reasons: (1) it was written to Christians in Rome, the capital of the world; and (2) it is the world’s first systematic, logically organized Christian theology. Ever since, every orthodox Christian theologian has elaborated the same two essential themes as Romans: sin and salvation, the “bad news” and the “good news.” Chapter 8 is, I think, the very best news, the most exalted and joyful chapter ever written.

Peter Kreeft, You Can Understand the Bible