What is the basis upon which social classes are built in Islam, how are they formed, and to what extent do they exist?

Islamic Sharia does not recognize class distinction; rather, it equalizes people in rights. The rich and the poor, the noble and the humble are all equal. The sole basis for differentiation is piety, as confirmed by Allah Almighty's saying: (O mankind, indeed We have created you from male and female and made you peoples and tribes that you may know one another. Indeed, the most noble of you in the sight of Allah is the most righteous of you), and the Prophet, peace and blessings be upon him, said: (Indeed, there is no superiority for an Arab over a non-Arab, nor for a non-Arab over an Arab, nor for a red-skinned over a black-skinned, nor for a black-skinned over a red-skinned, except by piety). Piety is the value derived from revelation, and it alone is weighed in Allah's balance, manifested in worshipping Him alone, obeying Him, and avoiding His prohibitions.