Back when the St. Louis Cardinals had five returning starters, Shelby Miller's 2012 season landed him squarely in the gap between "Ready to turn heads at Spring Training"—the narrative that leaves you in AAA for a month or two, pending the expiration of either a struggling veteran or an arbitration clock—and "Ready to just get a job already." A terrible start and a strikingly efficient finish left his Pacific Coast League numbers looking great, except for an Eric-Miltonian home run rate, and his MLB debut was great, if overshadowed by Trevor Rosenthal's hail-mary introduction to the bullpen.
Now that the Cardinals have four returning starters, his 2012 season lands him squarely in competition with Rosenthal and Joe Kelly, who beat him up to the majors while Miller was applying to get his pitch-calling privileges reinstated.
Shelby Miller's performance in 2013, after his confusing but ultimately promising 2012, has always been important to the Cardinals, but after Chris Carpenter's injury he's become an explicit part of their plans. They're high enough on Rosenthal that I wouldn't be surprised to see him sneak into the front of the pack for this particular opening, but pending an upset like that it's no longer enough for Miller to just turn heads in Spring Training.