Final answer:
The author emphasizes that Dr. Brock will talk about writing as an avocation to highlight the passion-driven nature of writing outside of professional constraints. The distinction may ultimately not be as important to Zinsser, who values the dedication to writing irrespective of its classification as a hobby or profession.
Step-by-step explanation:
The author points out that Dr. Brock was going to talk about writing as an avocation rather than a vocation to distinguish between writing as a hobby or secondary pursuit and writing as a main profession. This difference matters to the author because it frames writing as a personal choice driven by passion rather than just a job. It is implied that for William Zinsser, after their talk, the distinction between avocation and vocation may not matter as much, as he recognizes the dedication and serious approach one can have towards writing regardless of its categorization in one's life.
In this conversation, writing as an avocation can involve deep commitment and not merely casual engagement, a sentiment that could align with Zinsser's views. The shift from viewing writing purely as a profession to recognizing its value in one's personal life highlights the importance of pursuing activities for their intrinsic rewards rather than just their economic benefits. Thus, for anyone passionate about writing, the distinction between avocation and vocation becomes less significant as the real focus is on the quality and significance of the writing itself.