What does Deuteronomy 25:9 mean?

Then the widow will go up to him in front of everyone, take off his sandal, spit in his face, and say, 'This is what happens to a man who won't build up his brother's family.' Deuteronomy 25:9 - Modern Text Bible

(This public act shames the man for not fulfilling his family duty, making it clear to everyone.)