30 juz' (plural ) can be used to read through the entire Quran in a month. Some of these parts are known by names—which are the first few words by which the begins. A is sometimes further divided into two ḥizb (plural ), and each subdivided into four . The Quran is also divided into seven approximately equal parts, manzil (plural ), for it to be recited in a week. A different structure is provided by semantic units resembling paragraphs and comprising roughly ten each. Such a section is called a rukū`. The Muqattaʿat ( , 'disjoined letters, disconnected letters'; also 'mysterious letters') are combinations of between one and five Arabic letters figuring at the beginning of 29 out of the 114 chapters of the Quran just after the basmala. The letters are also known as fawātih (), or 'openers', as they form the opening verse of their respective suras. Four surahs are named for their : Ṭāʾ-Hāʾ, Yāʾ-Sīn, Ṣād, and Qāf. The original significance of the letters is unknown. Tafsir (exegesis) has interpreted them as abbreviations for either names or qualities of God or for the names or content of the respective surahs. According to Rashad Khalifa, those letters are Quranic initials for a hypothetical mathematical code in the Quran, namely the Quran code or known as Code 19. According to one estimate the Quran consists of 77,430 words, 18,994 unique words, 12,183 stems, 3,382 lemmas and 1,685 roots. Contents The Quranic content is concerned with basic Islamic beliefs including the existence of God and the resurrection. Narratives of the early prophets, ethical and legal subjects, historical events of Muhammad's time, charity and prayer also appear in the Quran. The Quranic verses contain general exhortations regarding right and wrong and historical events are related to outline general moral lessons. Verses pertaining to natural phenomena have been interpreted by Muslims as an indication of the authenticity of the Quranic message. The style of the Quran has been called "allusive," with commentaries needed to explain what is being referred to—"events are referred to, but not narrated; disagreements are debated without being explained; people and places are mentioned, but rarely named." Monotheism The central theme of the Quran is monotheism. God is depicted as living, eternal, omniscient and omnipotent (see, e.g., Quran , , ). God's omnipotence appears above all in his power to create. He is the creator of everything, of