I'm writing my Thesis and I found a brilliant book that helps me write it in a coherent manner. Consider this:
The author, Smith, talks about Approach XYZ and writes:
XYZ is about ..., first used by , that has more or less four common themes, theme A , theme B , theme C  and theme D .
So in my Thesis i say.
We will align with XYZ. As explained by Smith  (For whom we assign the reference  for the purpose of this question), there are four themes, and they are relevant to our study because bla bla bla. .
So my question is this.
Do I need to cite everyone? Or would citing Smith, who in turn cited everyone be sufficient?
Or is there no clear cut line? Perhaps I only need to cite those themes where I go beyond what Smith writes in his book or how they are affecting me directly?