What was the key purpose of the market days in philadelphia?

To provide goods to people with more safety and sanity.

Explanation:

Actually, the initial reason of that market was safety and sanity. Nowadays they still are operating but with less merchants. They offer some goods for people in general like fresh meats, fish, artisan cheese, groceries, flowers, grilled cheese, baked goods, crafts, books, clothing, and specialty and ethnic foods.

The Gulf of Tonkin Resolution