What advise does Mrs. Jones give to Roger at the end of the story?

"Thank you, M'am" is a short story by Langston Hughes (1902–1967) with an unexpected and thought-provoking twist on the meaning of punishment and unconditional love. When a teenage boy, Roger, attempts to steal the large purse of an elderly woman walking home from work late at night, he is very surprised. First he loses his balance and falls, and then the woman kicks him and drags him down the street. But she also asks him if there isn't anyone at home to tell him to wash his face. This question reflects an unexpected sense of concern for a would-be thief. Although the boy receives a punishment for his bad behavior, he is also humanized.
The woman, Mrs. Luella Bates Washington Jones, takes Roger to the small, furnished room she rents. She asks him why he tried to steal her purse, gives him supper, and gives him money to buy the blue suede shoes he hoped to purchase through the theft. The trust and humane treatment she provides to the misguided boy (in addition to a deserved punishment) allows Roger to see himself as both worthy and forgiven. Telling Roger to wash his face is an indirect way of showing him that someone does care about him. Mrs. Jones behaves like a wise relative who doles out both just punishment and unconditional love.
Mrs. Jones's parting words of advice to Roger are "Goodnight! Behave yourself, boy!" To these words Roger, who is dumbstruck by the events of the evening, can only manage to reply, "Thank you, M'am."