•Why it earns a slot
Mill's essay is the canonical short statement of utilitarian ethics, introducing the crucial distinction between higher and lower pleasures, grounding moral obligation in social feeling, and providing the most influential attempt to reconcile justice with the greatest-happiness principle.
Mill defends utilitarianism, the doctrine that actions are right insofar as they promote happiness and wrong insofar as they produce its opposite. He clarifies common misconceptions, argues that pleasures differ in quality as well as quantity, addresses the sources of moral obligation, offers a quasi-proof that happiness is the sole ultimate end, and finally reconciles justice with utility by showing that justice names the most vital class of utility-based moral rules.
This distillation is written from the freely available original, which is always the better read when you have the time: gutenberg.org.