Badlwin uses the paradox to emphasize the rage buried beneath his father's outward appearance and actions.
Explanation:
All right, first of all, we need to remember what we are talking about and explain the context in it's the best way.
In this question, we are talking about an excerpt from Notes of a Native son. In which Baldwin narrates a very elaborated behavior by the father. Explaining first the father's opinion about the people in the matter "the bill's collectors" and then describing how the father behaved to them. Portraying him as a wonderful actor that used all his true feelings to do the exact opposite to them of what he felt. So the more he despised them the better he treated them that is why he calls the father vindictively polite.
The kind of language that Baldwin used in order to make an emphasis on the rage in regard to his father's outward appearance and actions would then be he used the paradox vindictively polite. Hope this answer would be of help.
