What's our primary duty ?

Assalam O Alikum

Hadhrat Nuúmaan bin Basheer (Radhiallaahu Ánhu) says that Rasulullah (Sallallaahu Álayhi Wasallam) gave an example of people sailing on a boat having an upper deck and a lower deck. The people from the lower deck require water and request water from the people of the upper deck. The people from the upper deck refuse water so the people from the lower deck decide to make a hole on the floor of the ship and get water from the sea. Rasulullah (Sallallaahu Álayhi Wasallam) said, "If the people from the upper deck don't stop the people at the bottom from making a hole, the ship will sink and all the people travelling will drown." (Mishkãt vol. 2 p. 436)
Similarly, if people do not prohibit evil and sin in the society, the entire society - innocent and evil - will equally suffer.

Hadhrat Abu Hurayra (Radhiallaahu Ánhu) states that Rasulullah (Sallallaahu Álayhi Wasallam) said, "Command good and prohibit evil or else Allah will send such a punishment that will destroy everyone." (Ibid)