وَإِذَا رَأَيْتَ الَّذِينَ يَخُوضُونَ فِي ايَاتِنَا

And when you see those who engage in false conversation about Our verses (of the Qur'an),

by denying and mocking them.
The Prohibition of Sitting with Those Who Deny and Mock Allah's Ayat 

Allah said,
 
فَأَعْرِضْ عَنْهُمْ حَتَّى يَخُوضُواْ فِي حَدِيثٍ غَيْرِهِ

stay away from them till they turn to another topic.

until they talk about a subject other than the denial they were engaged in.
 
وَإِمَّا يُنسِيَنَّكَ الشَّيْطَانُ

And if Shaytan causes you to forget..., 

This command includes every member of this Ummah. No one is to sit with those who deny and distort Allah's Ayat and explain them incorrectly.

If one forgets and sits with such people,
 
فَلَ تَقْعُدْ بَعْدَ الذِّكْرَى

then after the remembrance sit not you,

after you remember,
 
مَعَ الْقَوْمِ الظَّالِمِينَ
 
 

in the company of those people who are the wrongdoers.

A Hadith states,

رُفِعَ عَنْ أُمَّتِي الْخَطَأُ وَالنِّسْيَانُ وَمَا اسْتُكْرِهُوا عَلَيْه

My Ummah was forgiven unintentional errors, forgetfulness and what they are coerced to do.

The Ayah above (6:68) is the Ayah mentioned in Allah's statement,

وَقَدْ نَزَّلَ عَلَيْكُمْ فِى الْكِتَـبِ أَنْ إِذَا سَمِعْتُمْ ءَايَـتِ اللَّهِ يُكَفَرُ بِهَا وَيُسْتَهْزَأُ بِهَا فَلَ تَقْعُدُواْ مَعَهُمْ حَتَّى يَخُوضُواْ فِى حَدِيثٍ غَيْرِهِ إِنَّكُمْ إِذاً مِّثْلُهُمْ

And it has already been revealed to you in the Book that when you hear the Verses of Allah being denied and mocked at, then sit not with them, until they engage in a talk other than that; (but if you stayed with them) certainly in that case you would be like them. (4:140),

for, if you still sit with them, agreeing to what they say, you will be just like them.

Allah's statement