Tawhid (Arabic: ‘making one,’ ‘asserting unity’) is the central theological concept of Islam: the absolute oneness and uniqueness of God (Allah). The Shahada — ‘There is no god but God, and Muhammad is his messenger’ — is the fundamental assertion of tawhid. Tawhid has three classical dimensions: unity of God’s lordship (rububiyya — God alone is creator and sovereign); unity of God’s names and attributes (asma wa sifat — God’s attributes are unique and cannot be compared to creation); and unity of worship (uluhiyya — worship belongs to God alone, making any worship of other than God the sin of shirk, polytheism). Shirk is the one unforgivable sin in the Quran (4:48). The entire Quran can be read as an extended meditation on tawhid — the radical monotheism that distinguishes Islam from all forms of polytheism and from the Christian Trinity, which Islamic theology understands as compromising divine unity.