وَأَنذِرْ بِهِ ٱلَّذِينَ يَخَافُونَ أَن يُحْشَرُوٓا۟ إِلَىٰ رَبِّهِمْ لَيْسَ لَهُم مِّن دُونِهِۦ وَلِىٌّ وَلَا شَفِيعٌ لَّعَلَّهُمْ يَتَّقُونَ
"Warn with it those who fear that they will be gathered to their Lord — they have neither protector nor intercessor besides Him — that they may guard themselves."
The same condition was treated at Fāṭir 35/18 (innamā tundhiru'lladhīna yakhshawna rabbahum bi'l-ghayb) and it was recorded there: the effect of the warning is tied to a condition on the side of the one addressed. I rely on that treatment.
And the verse's link with the next verse is worth recording: verse 52 begins with wa lā taṭrudi'lladhīna yadʿūna rabbahum. Two verses one after the other: one says who is to be warned, the other who is not to be driven away.