Working, even if it’s good work, is for money to live. If it’s satisfying and useful, well, that’s nice.
Volunteering is where you provide your little brick in the wall that helps the community.
Litmus test: if you had no need for money, would you still do the work? Nope. If you had no need for money, would you still volunteer? Probably.
The standalone statement by CS is true. But it does not follow from his logic. I would prefer “…it is unnecessary for some…”. One can provide extra value to the community by being empathetic and positive in one’s daily interactions. Further, explicit volunteerism and charity can simply be checkmarks of empty virtue. On the other hand, worker ants simply doing their job are not virtuous.
Some types of community service work provides more value than their own revenue supports. If you can volunteer for them I think you add more than just spending “well” (avoiding causing negative externalities ignored by price) and behaving lawfully.