Much has been made of the retirement of Brian Urlacher, the turning-over of the defense to Mel Tucker and his statements to use the same scheme in 2013.
Of course, ideally, the defense maintains its extremely high level of play from 2012, with largely the same personnel. They're potentially returning nine starters (or at least starting nine players who were on the team last year, Shea McClellin), including Lance Briggs and the back four of Tim Jennings, Charles Tillman, Chris Conte and Major Wright.
But as with the majority of defensive success in the NFL, the defense's success is carried through the defensive line, and particularly with a scheme predicated on forcing offenses to take the short plays in front of them and trying to force careless mistakes and turnovers.
I realize this states the obvious in many ways, but there are still a fair amount of questions for the defensive line as to the amount of success they'll have. Julius Peppers isn't getting much healthier or younger. Can Shea McClellin take a step forward that he'll absolutely need to take? Henry Melton's playing for a long-term deal either in Chicago or elsewhere - can he continue to grow as the penetrating, pass-rushing three-tech the defense needs?
When the Bears get pass-rush consistently, it's that much easier for the back seven of the defense to do their jobs, especially with the complete reworking of the linebacking corps that took place this offseason.
The defense can still be a top ten unit, and if the offense takes some strides, the Bears absolutely could be a playoff contender in 2013. But if the defense is that good, it'll be because the defensive line is making their own strides.