Why is the theme forgiveness?

Forgiveness can be considered a theme in Langston Hughes's "Thank You, Ma'am" as it is clearly demonstrated in the story. Roger is a boy that makes a mistake in trying to steal the purse of Mrs. Luella Bates Washington Jones. Mrs. Jones holds him in a "half-nelson" and takes him to her home all the while rebuking him for his poor choice.
When they arrive at her home, she lets go of Roger and orders him to wash his face. The door is left open, which gives Roger an opportunity to run. Instead, he does as he is told. Mrs. Jones then asks Roger if he's hungry and tells him he'll eat dinner with her. Roger again observes the open door and again chooses to stay.
Mrs. Jones admits there were times when she wanted things and she shares, "I have done things, too, which I would not tell you, son—neither tell God, if he didn’t already know." Through her comment and her actions, she lets Roger know that while she is holding him accountable, she also forgives him. When Mrs. Jones goes to prepare dinner, and Roger has his second opportunity to run, the author shares that Roger "did not trust the woman not to trust him." It is because she forgives him, and because she allows him the opportunity to be trusted, that he is trustworthy.