The answer to this question posed in the title of this post depends on what kind of person you are. If you're someone that is very optimistic about the future then you would probably say that beating the Cardinals isn't absolutely necessary. Is a win desired? Of course. But is you're optismitic, then your thinking means that a loss here doesn't completely kill the season.
Optimistic fan, meet fear everything fan. I'll admit, I tend to be more like the fear everything fan as I just am really not sold on the Lions yet. That may sound bad, but after watching this team long enough, you just automatically begin to figure the worst can and will happen. This line of thinking may be unfair to Rod Marinelli as he has coached this team to a great season so far, but the key thing there is so far.
I'll stop sounding so negative as I hate thinking that way, but realistically looking down the road, Detroit has to win games against teams like Arizona. With the schedule being so tough in the second half of the year, these games that should be won have to be won. If we ever want to see this team play beyond December, then a loss to a team like Arizona can't happen. Of course, there's always the chance that Detroit would lose this Sunday and then would pull off an upset or two against teams they shouldn't beat, but this is the Lions. Once again, I am reverting back to that line of thinking simply because it is just the way things have been, but a win against Arizona would help me to become less pessimistic.
In the grand scheme of things, a game against the Cardinals may not seem that important, but it really is for a few reasons. As I already said, with a schedule like the Lions have in the second half of the year, games against teams like Arizona have to result in wins. Secondly, a win on Sunday gets to Detroit to 7 on the year, meaning that the Lions finally can guarantee a season resulting in less than 10 losses. Thirdly, if the Lions want to contend for a division title or for a spot in January to keep playing beyond the regular season, then every game counts. That has never been more true than it is right now. Sure, games against the Packers will be more important due to the division ramifications, but these trap games can be just as deadly to title hopes.