“ARCing” is a method for tracing the argument of a passage in Scripture. It has its origins in Daniel P. Fuller, a professor at Fuller Seminary, and John Piper (who studied with Dr. Fuller). Dr. Tom Schreiner has written a very helpful book that explains both diagramming and ARCing called Interpreting the Pauline Epistles (Guides to New Testament Exegesis). ARCing is taught and used heavily at The Bethlehem Institute (now incorporated, I believe, into the Bethlehem College and Seminary) where I apprenticed from 2005-2007.
Now there is a nifty website dedicated to ARCing. Registration is $10/year or whatever you can afford. Here’s a short video of John Piper explaining what ARCing is and why it is helpful: