Allah says:

[أَفَمَن شَرَحَ اللَّهُ صَدْرَهُ لِلإِسْلَـمِ فَهُوَ عَلَى نُورٍ مِّن رَّبِّهِ]

(Is he whose breast Allah has opened to Islam, so that he is in light from his Lord) means, is this person equal to the one who is hard-hearted and far from the truth This is like the Ayah:

[أَوَمَن كَانَ مَيْتًا فَأَحْيَيْنَـهُ وَجَعَلْنَا لَهُ نُورًا يَمْشِي بِهِ فِى النَّاسِ كَمَن مَّثَلُهُ فِي الظُّلُمَـتِ لَيْسَ بِخَارِجٍ مِّنْهَا كَذَلِكَ]

(Is he who was dead and We gave him life and set for him a light (i.e. Belief) whereby he can walk amongst men -- like him who is in the darkness (i.e., disbelief) from which he can never come out) (6:122) Allah says:

[فَوَيْلٌ لِّلْقَـسِيَةِ قُلُوبُهُمْ مِّن ذِكْرِ اللَّهِ]

(So, woe to those whose hearts are hardened against remembrance of Allah!) meaning, they do not become soft when Allah is mentioned, and they do not feel humility or fear, and they do not understand.

[أُوْلَـئِكَ فِى ضَلَـلٍ مُّبِينٍ]

(They are in plain error!).

[اللَّهُ نَزَّلَ أَحْسَنَ الْحَدِيثِ كِتَـباً مُّتَشَـبِهاً مَّثَانِيَ تَقْشَعِرُّ مِنْهُ جُلُودُ الَّذِينَ يَخْشَوْنَ رَبَّهُمْ ثُمَّ تَلِينُ جُلُودُهُمْ وَقُلُوبُهُمْ إِلَى ذِكْرِ اللَّهِ ذَلِكَ هُدَى اللَّهِ يَهْدِى بِهِ مَن يَشَآءُ وَمَن يُضْلِلِ اللَّهُ فَمَا لَهُ مِنْ هَادٍ ]

(23. Allah has sent down the Best Statement, a Book, its parts resembling each other, (and) oft-repeated. The skins of those who fear their Lord shiver from it. Then their skin and their heart soften to the remembrance of Allah. That is the guidance of Allah. He guides therewith whom He wills; and whomever Allah sends astray, for him there is no guide.)