“You who believe, obey God and the Messenger, and those in authority among you. If you are in dispute over any matter, refer it to God and the Messenger, if you truly believe in God and the Last Day: that is better and fairer in the end” (Quran, 4:59).
Muslims are united in one ummah, or community, by their common testimony to the unity of God and the prophecy of Muhammad. Within this unity there is also diversity, reflecting differences of interpretation of Quran and ḥadīth, which led to debates about the nature of political authority, spiritual leadership, and the development of various schools of jurisprudence. Muslims have interpreted the paradigm of the Prophet in many ways, each emphasizing particular aspects of his life and teachings. These traditions both complement and sometimes contradict one another, thus weaving the rich tapestry of Muslim piety.
Perhaps the most significant division of Muslims is between those groups known as Shi‘a and those known as Sunnis. The initial split involved a dispute over who should assume Muhammad’s role of leading the community after his death, what type of authority this person should have, and what its scope and basis should be. These differences led to the initial development of varying systems of law and theology.
Drawing on the model of Muhammad’s close relationship with God and his mystical experiences and devotional practices, a crystallization of the mystical and esoteric dimension of Islam also emerged in the early centuries of Islam. Known today as Sufism [taṣawwuf], this movement became instrumental in the spread of Islam to all parts of the world. Sufism transcends many of the divisions in Islam, its organizations and artistic expressions inspiring Muslims to greater spiritual awareness.
An important stream of Islamic tradition developed around the model of Muhammad as interpreter of religious and legal doctrine, which came to be called sharī‘ah, the “path” or “way.” Sharī‘ah represents the moral and ethical values that enable Muslims to follow the will of God in accordance with the paradigm of the Prophet. After the death of the Prophet, a group of scholars, or ulamā, emerged. Some of these scholars established major schools of fiqh [jurisprudence], the laws derived from the sharī‘ah that determine how those moral principles should be applied.