Fables are characterized by having a moral to the story. Here, Aesop says that those who mistreat others with their cunning can expect to eventually suffer later themselves.
Fox wanted to amuse himself so he invited Stork to lunch. He served his guest a thin soup in a shallow bowl knowing Stork would not be able to eat it with her long beak.
Fox secretly smiled as they parted knowing Stork was still hungry. But Stork graciously thanked her host for his hospitality and invited him to her place for a meal the next week.
On this occasion shop was served in a vessel with a long narrow neck which was easy for Stork to use but Fox could get nothing but drips to lick. Fox left knowing he had been paid back for his unkind trick and would go to bed hungry that night.