In the interests of deeper analysis (and because I'm not really sure how a game analysis can be summed up in three items), instead of just one Three Keys post, I'll split it up into three offensive and three defensive keys. Defensive now, obviously, and I'll do offensive a little later today.
1) Does the return of Chris Harris put a stop to Brandon Meriweather's freelancing?
Um, no. I'm not sure what at this point will stop Meriweather from abandoning his responsibilities (I mean, if previous fines and being cut from a Belichick team didn't get the message across...), but Harris outclasses any safety on the Bears' roster in terms of coverage, and he actually can hit hard while still making the tackle, so at the least there will be some semblance of stability at the back end. And going against this fast-rising offensive corps, good safety play will be paramount to a better defensive showing which just hasn't been there.
2) How the flip do the Bears stop Calvin Johnson?
You don't "stop" Megatron; you hope to slow him down enough so he has no impact. Barring a Stafford injury (and no, I don't ask for injuries), and even with that, Johnson simply does not get shut down. The problem is that the Bears don't really have a secondary that can win a jump ball against a Johnson-type receiver - remember, it's basically the Smurfs and Peanut Tillman. That being said, Johnson was slowed down just enough in week 1 last season, so maybe the Bears have something in their pocket. Tillman will be one part of the equation, and I expect at least a bracket or deep safety over the top every time. Beyond that, maybe a trampoline, make those jump balls really interesting.
3) We were promised a penetrating defensive line! When does the delivery truck come?!
Anyone around my age, definitely older, I'm sure knows Marvin the Martian. I remember in one of his cartoons he says "Where's the kaboom? There was supposed to be an earth-shattering kaboom!" That's how I feel about our defensive line right now. There was supposed to be a QB-rattling, powerful, penetrating kaboom - I mean defensive line. Apparently it was here for one game (Atlanta), and then must have gone into hibernation or the D-Line Bus got lost. Wherever it is, I hope it shows up soon. This isn't a great Detroit offensive line, but it's good enough to get the job done, and now would be a good time for Peppers to atone for whatever that showing was against Carolina by picking up a sack or two working against Jeff Backus. Melton too. And what's Idonije's deal - is the book out on him, or is he just not good enough, because he has put on quite the disappearing act this season so far.
That's all I've got for the defensive side of the ball; I'll have the offensive side up a little later.