When Hisham ibn Hakam asked Imam Sadeq (AS) about the philosophy of fasting, Imam (AS) replied:

Truly, Allah (SWT) made fasting Wajib in order to establish equality between the poor and the rich. The rich ones have never felt the pain of hunger and poverty, and whenever they want to eat or drink, those will be provided for them. Therefore, Allah (SWT) made fasting Wajib in order to create equality between God’s servants from the poor and the rich; in order that the wealthy ones can feel the hunger and the pain of the poor ones, and the wealthy show kindness and compassion toward the poor [1].

[1] Man la Yahdhrahul Faqih, Vol. 2, Page 73.

Source: en.shafaqna.com