Who is Zinsser's Parents from On Writing Well and what is their importance?

Zinsser's parents hover over all his work. His mother loves good writing, and his father keeps strong work ethics. The result is that the author loves to produce good writing, no matter how much work that takes, and he has no choice but to produce the best writing he can. He mentions his parents in passing, but that does not diminish their influence. It shows in his finished product.