Among all the amazing gifts Islam has given us, one is the notion of Fard Kifaayah.
One simple way to understand this most amazing Islamic concept is to look at a positive as well as a negative joint social and moral -- and in some cases legal -- responsibility that may fall on the shoulders of a group, community, nation or society.
And that joint responsibility or collective duty or shared obligation may take two forms:
(A) To do what is good and right, and, at the same time, to require others also to do what is good and right.
The Qur'an calls this Amr Bil-Ma'roof: Telling others to do good things. And it is a fundamental Islamic social and moral obligation.
(B) To abstain from doing what is bad and evil, and, at the same time, to require others also to stay away from doing what is bad and evil.
The Qur'an calls this Nahyi 'Anil Munkar: Telling others to keep away from doing bad and wrong and evil things.
And this is also a shared social and moral obligation in Islam.
And according to the Qur'an, it is the very reason why God raised up the Believers as a nation and declared them to be the Best Nation and the Best People on earth: Because they have been commissioned by God to do good and tell others to do good, and to stay away from doing what is bad and tell others also to stay away from what is bad.
Muslims, from time to time, give up this duty -- this Divine Mandate of Amr Bil-Ma'roof and Nahyi 'Anil Munkar -- and, as a result, suffer the consequences that become obvious for all to see.