The Sarvastivada Abhidharma also used these, along with a fifth category: "factors dissociated from thought" (cittaviprayuktasaṃskāra). The Sarvastivadas also included three dharmas in the fourth "unconditioned" category instead of just one, the dharma of space and two states of cessation.
The ultimate goal of the Abhidharma is Nirvana and hence the Abhidharmikas systematized dhammas into those which are skillful (kusala), purify the mind and lead to liberation, and those which are unskillful and do not. The Abhidharma then has a soteriological purpose, first and foremost and its goal is to support Buddhist practice and meditation. By carefully watching the coming and going of dhammas, and being able to identify which ones are wholesome and to be cultivated, and which ones are unwholesome and to be abandoned, the Buddhist meditator makes use of the Abhidharma as a schema to liberate his mind and realize that all experiences are impermanent, not-self, unsatisfactory and therefore not to be clung to.
Another important project for the Abhidharmikas was to outline a theory of causality, especially of how momentary dharmas relate to each other through causes and conditions.