Abhidhamma Studies is one of those books that you can reread every few years to find new depth.
In this work Nyanaponika Thera displays great insight into the many layers of knowledge that can be found within the first beneficial citta mentioned in the Abhidhamma Piṭaka.
And if you don’t want to read the whole work, the introduction alone is well worth reading.
In the introduction, Nyanaponika Thera writes how the Abhidhamma represents the core of Buddhist philosophy through its analysis and synthesis, namely that reality consists of separate impermanent moments in which there is no underlying self, no ‘I’ (anattā), while there is a cause-effect relationship between these moments that, for example, make meditation and moral behaviour necessary for liberation.
We explain this further in our text A Short Introduction to Abhidhamma.