Do you that "A&P" focuses on the feelings of loneliness and isolation that lead Sammy to seek some form of higher truth or ultimate meaning?
I think this is definitely true to a certain extent. There is a real sense in which Sammy is presented as a young man who is profoundly alienated against society and the people that he serves as part of his job. We need only look at the way in which he describes the people that he interacts with to see this in action. The first customer that he describes as the girl enters he describes as being "a witch about fifty" and a "cash-register-watcher." Note how he describes the scene as the girls in their bathing costumes walk down the aisles:
The sheep pushing their carts down the aisle--the girls were walking against the usual traffic (not that we have one-way signs or anything)--were pretty hilarious... I bet you could set off dynamite in an A & P and the people would by and large keep reaching and checking oatmeal off their lists...
He refers to customers as "sheep" and talks about the "one-way" system in the shop to show how he thinks of society as being a set of rules that instills conformity and oppression rather than freedom and liberation. Sheep are of course notorious for following each other around and not being able to assert themselves. This is supported by his reference to housewives as "houseslaves" as if to confirm his view of society as something that compels slavish obedience in its adherents. These are ways in which Sammy is presented as being a young man who is disenchanted with society and profoundly isolated and unable to connect with those around him.