وَمَا عَلَى الَّذِينَ يَتَّقُونَ مِنْ حِسَابِهِم مِّن شَيْءٍ

There is no responsibility for them upon those who have <b>Taqwa</b>,

means, when the believers avoid sitting with wrongdoers in this case, they will be innocent of them and they will have saved themselves from their sin.

Allah's statement,
 
وَلَـكِن ذِكْرَى لَعَلَّهُمْ يَتَّقُونَ
 
 

but (their duty) is to remind them, that they may avoid that.

means, We commanded you to ignore and avoid them, so that they become aware of the error they are indulging in, that they may avoid this behavior and never repeat it again