The Islamization of Iran after the Arab conquest was possibly more far-reaching in its effects than were the linguistic changes. The Iranian religion prior to that time was Zoroastrianism, which was based on the belief that there was an eternal struggle between the forces of good and evil. Shiism became the national religion of Iran during the sixteenth century, at which time the ulama began to play an important role in the social and political life of the society. When Ayatollah Khomeini led the revolution that toppled the shah in 1979, he declared that the ulama were needed to purify Islam and apply its laws. As an Islamic republic, Iran is guided by the tenets of Islam as interpreted by the ulama. Most Persians today are Shia Muslims of the Ithna Ashari sect and adhere to Islamic laws and principles.
Persian art is found in a variety of forms ranging from intricately patterned tiles and Quranic inscriptions on the walls of mosques to handicrafts, miniature painting, and calligraphy. Poetry with well-defined meter and rhyme is a popular Persian art form. Persian poetry often deals with subjective interpretations of the past and sometimes satirizes social problems such as inequality, injustice, and repression.
A popular religious or philosophical theme that is expressed in Persian literature is qesmet, or fate. Persians believe that all unexplainable occurrences are the will of God, and that most things in life are controlled by fate rather than by humans. The unpredictable nature of life is sometimes used to justify the pursuit of pleasure.