With all respect to the previous two editors, perhaps one can say that "A & P" has no real "message," but is rather an insightful sketch of teenage attitudes and behaviors.

The girls seem unaware of the social norms that they are violating; the boy is moved to an impulsive, self-destructive act by force of his confused sexual yearnings; throw all this together with the boy's rebellion against his parents' middle-class values of working hard and keeping your mouth shut, and you've got a perfect picture of a typical bunch of teenagers.

Now, I don't mean that there really is no message.  I do mean that there is much to learn from this story without searching for a "moral."

In my opinion, the message of this story is that it is important to be yourself, but you have to realize that being yourself has consequences in the real world.

I think that the story is about individualism.  The girls (or at least Queenie) are expressing themselves by the way they are dressed.  Sammy wants to express himself by defying his boss and by acting out against the social values and conventions that his boss is personifying.  To the extent that he makes the girls and Sammy sympathetic, Updike seems to be telling us that it is good to be yourself.

But the message is mixed some.  Neither Sammy nor the girls comes out of this 100% happy.  Both are punished in some way for choosing to be individualistic.  This says to me that part of the message is that we may have to pay the price for choosing to go against society.