While I agree with most of this, let me refine a few of the points.
First, if you attend a top 5 law school, your first year grades don't even matter that much when it comes to getting a law firm job (even at a national, prestigious law firm). You know the old joke, what do you call someone who finishes last in his class at Harvard Law School? A Harvard Law graduate.
Second, your second and third year grades DO matter if you are interested in obtaining a federal court clerkship. These clerkships typically are for a year with a judge at either the district court or appellate court. They are considered to be VERY presitgious and will be a nice marker on your resume. But the judges DO care about how you've done throughout your law school career, not just your first year grades.
Finally, there is no question that you will work HARD at a law firm job. If you are not interested in working hard, please do not go to law school.
This is definitely true - I should have mentioned that I was speaking as someone who only had an interest in going to a large firm and making a lot of money. I never once even considered a clerkship because I don't ever want to be a litigator or visit a courtroom and I needed money ASAP after graduation.