According to search-discovered classical Islamic scholarship, Arrogance (al-Istikbar) is the quintessential spiritual disease and the root of disbelief, defined as the rejection of divine truth due to an internal feeling of superiority (kibr). The Quran establishes its archetype in the story of Iblis, who refused Allah's command to prostrate to Adam out of pride, declaring 'I am better than him' (Quran 7:12). Imam Al-Ghazali describes it as a 'deadly poison' of the heart, as it is a direct challenge to the greatness that belongs only to Allah. This understanding is synthesized across 71 Quranic verses, where Ibn Kathir and Al-Tabari explain that the arrogance of past nations like that of Pharaoh was the primary cause of their rebellion against the prophets and their eventual destruction. Istikbar manifests not only in rejecting faith but also in disdainful social behavior, such as walking haughtily upon the earth (Quran 31:18), which is strictly forbidden. The ultimate consequence, confirmed by scholarly consensus, is being barred from Paradise and residing eternally in Hellfire, the designated abode for the arrogant.