Read the series.
The Best Commentaries on Romans: Remember, this list has preachers primarily in mind.
1. Douglas Moo (NICNT) — Somewhat dense, which may hinder readers somewhat, but interaction with the text and the literature is very impressive. Deals well with the ‘new perspective’, and even manages some applications (but see Moo’s contribution to the NIVAC series). His Introduction is on the short side, but there are numerous excurses. Not all will like his treatment of Chapter 7.