﴿ ذَٰلِكَ بِأَنَّهُمْ قَالُوا۟ لَن تَمَسَّنَا ٱلنَّارُ إِلَّآ أَيَّامًۭا مَّعْدُودَٰتٍۢ ۖ وَغَرَّهُمْ فِى دِينِهِم مَّا كَانُوا۟ يَفْتَرُونَ ﴾

“simply because they claim, "The fire will most certainly not touch us for more than a limited number of days": and thus the false beliefs which they invented have [in time] caused them to betray their faith.”

That turning away and rejection was because they said ‘the Fire shall not touch us except for a number of days’ that is for forty days only the length of time their forefathers worshipped the calf after which it would end; and the lies they used to invent in their saying this have deluded them in their religion wa-gharrahum fī dīnihim ‘it has deluded them in their religion’ is semantically connected to mā kānū yaftarūna ‘the lies which they used to invent’.