Seeing as one may not afflict any fellow-Jew, why does the Torah mention specifically a widow and an orphan?
Rashi and Rashbam: Because, on account of their vulnerability, people tend to take advantage of them. 1
Why does the Pasuk write "Kol Almanah ... "?
Ramban: To teach us that the prohibition applies even to a widow who is wealthy - because her tears too, flow easily and she is in a constant state of distres.