Your original question asked two questions and, according to enotes regulations, I have edited it down to one question. Please do not ask multiple questions.
To consider the question above, how do we respond to acts of random and unsought-for sacrificial kindness, as characterised by Mrs. Jones? One of the qualities that makes this story so powerful and memorable is that Mrs. Jones acts completely differently from how we would expect her to act. There aren't many people that would stop a thief and then take them home to share food with them, taking time to find out about their lives. It is surprise and shock that is expressed by Roger throughout the tale as he is dragged along and passively sits with Mrs. Jones, then said goodbye too before he is able to formulate a response or a way of saying thank you for such an unexpected act of kindness:
They boy wanted to say something other than "Thank you, m'am" to Mrs. Luella Bates Washington Jones, but although his lips moved, he couldn't even say that as he turned at the foot of the barren stoop and looked up at the large woman in the door. Then she shut the door.
It appears that, for some acts of kindness, there are no words to express how we feel and the gratitude that overwhelms us. The kindness of Mrs. Jones literally leaves Roger speechless, and he is not even able to stammer out the "Thank you" that he knows is insufficient.