CHICAGO -- And now, we see how the Eagles react to a different opponent and a game situation with jobs very much on the line. Welcome to the preseason opener, just in time for all of us.

The Eagles get it going at Soldier Field (8 PM, 6abc/94WIP) and, boy, is there a lot to watch. The starters are slated, tentatively of course, to play about 10-15 snaps. After that, the coaches will roll in players and keep moving combinations and seeing how the personnel packages work.

There are a couple of rules to remember about the preseason, so let's review here.

1. Do Not Overreact To Big Plays Or Mistakes

The schemes are going to be relatively simple as, we must remember, the objective of the preseason is to find the best 53 players on the roster. The only way to fairly evaluate players in an apples-to-apples method is to see how they play in base situations. So, for example, you aren't going to see Bill Davis dial up blitzes to free No. 1 draft pick Marcus Smith II off the edge. Instead, Davis wants to see Smith get off blocks, drop in coverage and play the edge in the running game. He wants Smith to learn from his mistakes and improve in New England next week.

Yes, the Eagles want to win the game and they want to play well, but the most important thing is to give the young players a chance to feel the speed and intensity of a preseason game and for the veterans to, as many of them say, "knock the rust off" in their first game action of the year.

2. Coaches Know The Players Have Wide Eyes

Here are key dates to remember: Rosters are trimmed to 75 players on August 26 and then reduced to 53 players on August 30. So players, for the most part, are going to have three preseason games to improve, to get things right.

Every single rookie is going to have a "Welcome-to-the-NFL" moment tonight. It just happens. It's an entirely new environment and a completely new game. So if rookies make mistakes, it's anticipated. The key times come following the game, in the days to follow, as coaches review the performances on film and work on corrections.

Next week, the Eagles practice for a few days with the Patriots and then play New England. That will be an awesome time to get a true gauge on a player's progress.

3. Finally, The Starters Won't Play A Lot

With only an exception or two or three around the league, the veterans see a handful of snaps in the preseason opener. For the Eagles, quarterback Nick Foles and running back LeSean McCoy are going to play tonight and they will have a chance to get right into the flow of games.

The starters aren't going to play beyond the first quarter, unless there are unusual circumstances. The starters want to get on the field, build some cohesion in a game and then get to the sidelines without any injuries.

It's a game for the backups, for jobs to be earned, for a roster to be sorted through. It's a welcome-back-to-football night for Eagles fans craving football.

It's a night to celebrate, and to understand the rules of the preseason.

Now, for some thoughts on the Eagles-Bears ...

• Big stage for Allen Barbre at right tackle as he makes his first start in place of Lane Johnson. Barbre has had a good summer and now lines up against an aggressive Bears front. Johnson, by the way, will play with the backups. He is eligible to play in all four preseason games.

• Arrelious Benn and B.J. Cunningham and all of the receivers who have been so good in the camp situation will stake their claim for roster spots tonight. Pencil in Jeremy Maclin, Riley Cooper, Brad Smith, Jordan Matthews and Josh Huff in for roster spots. Who is the sixth receiver?

• There is still very much a battle for the safety spot alongside Malcolm Jenkins. Nate Allen and Earl Wolff have shared reps, so the winner of the job could very well be decided in these preseason games.

• Can a longshot earn a roster spot at running back? Look for Henry Josey and David Fluellen to see quite a bit of time with Chris Polk sidelined and McCoy and Darren Sproles likely to see only a handful of reps.

• Mark Sanchez hasn't played in a game since the preseason last year when he suffered a shoulder injury that ended his year. He's ready to go, excited for the chance to play. "I'm really looking forward to it," he said. "I'm glad to be here in this situation and I'm going to make the most of it." We've seen quarterbacks resurrect their careers in Philadelphia before. Is Sanchez the next to thrive?