Religiosity describes the quality of being religious or of adhering to a religion. Religion describes a class of idea systems employed to explain events and distributions of power. Religions meet different needs in differnet societies. The only thing universal about religion is that it is universal in all human societies. Beyond that the content of religion varies immensely. Some posit the exitence of a god or gods or other supernatural beings while others do not. Monotheisms like Judaism, Christianity and Islam insist there is one god while Hinduism offers many gods while Buddhism and Jainism reject the importance of god or gods altogether. Some religions promise an afterlife and others do not. The monotheisms offer reward and punishment after death but many traditional folk religions ignore the possibility. Some religions offer moral or ethical codes but others like Shinto do not. Most religions designate orthodox practices, values, institutions, and rituals.
Religions appeared in pre-modern societies in large part because people lacked alternative idea systems to explain their world. They continue to be present in modern societies because they meet the need to give meaning, however absurd or false, to personal crises of life and death. Some people are so politically and socially disempowered that they crave non-rational explanations for events. Those who reject Darwinian evolution or believe they live in the millennial "end times" are a case in point. Some may be simply to lazy too think rationally. Certainly some people are always ready to exploit wishful thinking, as with "faith healing." Some cynical believe that religion is necessary to keep the ignorant and irrational masses in check.
Religious identity is often used as an ethno-national marker in the place of or in addition to language, race or common historical experience. Protestantism and Roman Catholicism are used as ethnic markers in Northern Ireland.