That means Epicurus holds a view of reality which says in effect humans are nothing more than vast collections of material atoms all which behave according to deterministic laws. His psychological hedonism is a consequence of this determinism. Thus human free will is an illusion. Really all our actions are just as determined as the motions of billiard balls on the billiard table. If this is the case, it makes no sense to say to someone that he should pursue natural necessary pleasures and should shun unnatural ones, for he is determined to do exactly what he is going to do from the start.
Epicurean ethics recommends withdrawal.
The Epicurean attitude towards involvement with public affairs was that it disrupts ataraxia or tranquility of soul. Thus Epicurus recommends withdrawing from the world and its problems. This is not a doctrine to produce revolutionaries or saints and martyrs.