question #2 Sahih al-Bukhari 1883, Book 29, Hadith 17 : How does the concept of a city expelling impurities relate to the spiritual development of individuals in Islam?

A bedouin came to the Prophet (ﷺ) and gave a pledge of allegiance for embracing Islam. The next day he
came with fever and said (to the Prophet (ﷺ) ), “Please cancel my pledge (of embracing Islam and of
emigrating to Medina).” The Prophet (ﷺ) refused (that request) three times and said, “Medina is like a
furnace, it expels out the impurities (bad persons) and selects the good ones and makes them perfect.”