Sincerity of the heart versus outward utterance

مَن كَفَرَ بِٱللَّهِ مِنۢ بَعْدِ إِيمَـٰنِهِۦٓ إِلَّا مَنْ أُكْرِهَ وَقَلْبُهُۥ مُطْمَئِنٌّۢ بِٱلْإِيمَـٰنِ وَلَـٰكِن مَّن شَرَحَ بِٱلْكُفْرِ صَدْرًا فَعَلَيْهِمْ غَضَبٌ مِّنَ ٱللَّهِ وَلَهُمْ عَذَابٌ عَظِيمٌ

Whoever disbelieves in [i.e., denies] Allāh after his belief... except for one who is forced [to renounce his religion] while his heart is secure in faith. But those who [willingly] open their breasts to disbelief, upon them is wrath from Allāh, and for them is a great punishment;