The words "acid" and "base" are functional terms, and not labels. They describe what a substance does, rather than what it is.
Von Handler is saying that nominal concepts like acid and base are better understood as the functional concepts acidity and basicity. Some things are better understood by what they do rather than what they are. So to get at what von Handler was trying to say, we just have to think about what acids and bases do and that's easy: they attract opposite polarity and they repel like polarity. In the natural world acids and bases polarize other molecules using attractive and repulsive forces to hasten change. Back here I wrote:
How nature really works (at a chemical level) is polarization followed by attack followed by depolarization.
Wish I could explain it better because it really is a simple concept.