Jared Allen watched as coaches delivered instructions just before his first practice as a Chicago Bear, and in the background images of past Bears-Vikings matchups flickered on the screen.

"I’m like, 'We were actually doing this,'" Allen said. “It was a little odd."

But once Allen actually put on that Bears jersey after so many years playing for the NFC North rival Minnesota Vikings, the veteran felt “like you’re a part of something special,” and he wants desperately to prove he is worth the club’s four-year, $32 million investment in him.

"Change is good if you allow it to be good. It definitely energizes you," Allen said. "For me, it’s the excitement of being part of something great. Minnesota was heading in a different direction than I thought my career, my life, my path is going. So I made the decision not to go back there. When I looked at the total equation, this was a place where I can be a part of something great. Personally, I don’t know if you call it selfishness or not, but I don’t want to be that guy who they feel like 'we shouldn’t have got him.' When I signed, I wasn’t going to be that guy that wasn’t worth the money."

Now Allen sets upon the task of proving it. Not that he hasn’t pretty much done that already with 128.5 career sacks, including seven consecutive seasons in which he posted double-digit totals. In 2011, Allen came within a half-sack of Michael Strahan's single-season record of 22.5 and made the Pro Bowl in four of his six years with the Vikings.

In a side-by-side comparison of Allen and Julius Peppers, who he’s replacing in the Bears' starting lineup, the former has played 580 more snaps than the latter over the past 64 games, with 48 more tackles, 19 more sacks and 22 more disrupted drop-backs.

“My motivation to be the best at what I do is a self-motivation,” Allen said. “It’s probably more of a fear of failing than it is necessarily thriving to be the best. I just want guys, when I leave this league, I want them to say, 'He did it the right way, he gave everything he had, and not one day he was stealing checks.' So that’s what motivates me. That’s what energizes me. I’ve got a full year now of training off my shoulder injury. Last year I couldn’t start working out until May. So I’m healthy; I feel good again. It’s exciting. There are new people. Even though you've played against these guys, you are trying to prove yourself to the coaching staff, to your teammates again to let them know they can trust my day-to-day habits and I’ll be ready to play on Sunday.”

How much he’ll contribute remains unclear. After all, Allen is 32, and over the past six years he’s played 93 percent of Minnesota’s snaps. Allen needs 4.5 sacks this season to move into sole possession of 10th place on the all-time sack leaders list. If Allen posts 13.5 sacks in 2014, he could move as high as No. 5 on the all-time list and pass Strahan.

Motivation certainly won’t be an issue for Allen.

“When you’re with a franchise with so much history, you don’t want to be that guy that 'he wasn’t a true Bear,'" Allen said. "So you try to put everything into it."