The nature of Muslim devotional life in Islam is rooted in its basic theological presuppositions. The three primary fundamentals of religion (uṣūl al-dīn) are tawḥīd (belief in the unity of God), nubūwah (belief in prophets), and qiyāmah (belief in the Day of Judgment). The acceptance of these three beliefs is required of all Muslims. Collectively, they constitute the essence of the Islamic worldview.

Tawḥīd is the core concept of Islam. The sovereignty of a monotheistic God, who is omnipotent, omniscient, and simultaneously transcendent and immanent, is Islam's definitive tenet. For Muslims there is one and only one true God, who is identical with the God of Abraham, Moses, and Jesus. The necessity of obedience to God's will is thus the foundation for all devotion in Islam. Every human being should aspire to live as a servant (ʿabd) of God. For...