According to classical Islamic scholarship, the concept of 'not Allah' encapsulates the foundational principle of Tawheed—the absolute, indivisible oneness of God. This principle begins with a negation, 'La ilaha' (there is no god/deity), before the affirmation, 'illa Allah' (except Allah), signifying that divinity and the right to worship are denied for all of creation and belong exclusively to the Creator. The Arabic term 'ilah' refers to anything that is worshipped or deified. The Quranic verses 5:17, 5:72, and 5:116 serve as critical applications of this principle, directly refuting the deification of Jesus, son of Mary. Classical commentators like Ibn Kathir explain that these verses correct the Christian belief in Jesus's divinity, labeling it as disbelief (kufr). The verses argue logically that Jesus, as a created being, cannot be God and that he himself preached pure monotheism. This synthesis, grounded in the Quran, establishes that attributing divinity to anyone or anything 'not Allah' constitutes shirk, the most grievous sin in Islam.