Muhammad’s religion eventually attracted great numbers of people, partly because of the straightforward nature of its doctrines. The strictly monotheistic theology outlined in the Qur’an has only a few central tenets: Allah, the Arabic word for God, is all-powerful and all-knowing. Muhammad, Allah’s prophet, preached his word and carried his message. Muhammad described himself as the successor of both the Jewish patriarch Abraham and Christ, and he claimed that his teachings replaced theirs. He invited and won converts from Judaism and Christianity.

Because Allah is all-powerful, believers must submit themselves to him. All Muslims have the obligation of the jihad (literally, “self-exertion”) to strive or struggle to lead a virtuous life and to spread God’s rule and law. In some cases, striving is an individual struggle against sin; in others, it is social and communal and could involve armed conflict, though this is not an essential part of jihad (jee-HAHD). The Islamic belief of “striving in the path of God” is closely related to the central feature of Muslim doctrine, the coming Day of Judgment. Muslims believe with conviction that the Day of Judgment will come; consequently, all of a Muslim’s thoughts and actions should be oriented toward the Last Judgment and the rewards of Heaven.

To merit the rewards of Heaven, a person must follow the strict code of moral behavior that Muhammad prescribed. The Muslim must recite a profession of faith in God and in Muhammad as God’s prophet. The believer must pray five times a day, fast and pray during the sacred month of Ramadan, and contribute alms to the poor and needy. If possible, the believer must make a pilgrimage to Mecca once during his or her lifetime. According to the Muslim shari’a (shuh-REE-uh), or sacred law, these five practices constitute the Five Pillars of Islam.

The Qur’an forbids alcoholic beverages and gambling, as well as a number of foods, such as pork, a dietary regulation adopted from the Mosaic law of the Hebrews. It condemns business usury — that is, lending money at interest rates or taking advantage of market demand for products by charging high prices for them.

Polygyny, the practice of men having more than one wife, was common in Arab society before Muhammad, though for economic reasons the custom was limited to the well-to-do. The Qur’an limited the number of wives a man could have to four. It also established a strict sexual morality and condemned immoral behavior on the part of men as well as women.

The Qur’an set out rules for inheritance, which privileged sons over daughters. Nonetheless, Muslim women of the early Middle Ages had more rights than Western women. For example, a Muslim woman retained complete jurisdiction over one-third of her property when she married and could dispose of it in any way she wished. Women in most European countries and the United States did not gain these rights until the nineteenth century.