I think his point (and the broader point being assumed by the author) was that "spending your time in activities that realize your self" does, in fact, feel a lot like work.
If your passion is painting, and its something you would do for free, then fulfilling your artistic potential is still work. It still requires hours upon hours of deliberate practice. The great masters would spend years working on a single painting. You don't think there would be times when they just didn't feel like making progress? Where they wanted to just take the day off and hang out at a bar with their friends?
Part of the human condition is struggle, imo. That's what I think the OP is getting at when he says that human beings need work. Maybe not a 9-5, but we all need something worth staving off instant gratification for.