This is a paragraph from the short story brownies by zz packer....

This is a paragraph from the short story brownies by zz packer. Based on this paragraph, What is it that Laurel "only then" understands about her father's motivations for doing this? (That is, why, according to Laurel, did her father do what he did?). can you explain? thank you

"I thought about it, and then remembered the words my father had said about them painting our porch, though I had never seemed to think about his words after he'd said them.

" 'He said,' I began, only then understanding the words as they uncoiled from my mouth, 'it was the only time he'd have a white man on his knees doing something for a black man for free.'

I now understood what he meant, and why he did it, though I didn't like it. When you've been made to feel bad for so long, you jump at the chance to do it to others. I remembered the Mennonites bending the way Daphne had bent when she was cleaning the restroom. I remembered the dark blue of their bonnets, the black of their shoes. They painted the porch as though scrubbing a floor. I was already trembling before Daphne asked quietly, 'Did he thank them?'

I looked out the window. I could not tell which were the thoughts and which were the trees. 'No,' I said, and suddenly knew there was something mean in the world that I could not stop."  (527-528)