وَلَوْ شِئْنَا لَآتَيْنَا كُلَّ نَفْسٍ هُدَاهَا وَلَٰكِنْ حَقَّ الْقَوْلُ مِنِّي
لَأَمْلَأَنَّ جَهَنَّمَ مِنَ الْجِنَّةِ وَالنَّاسِ أَجْمَعِينَ
13. And if We had willed, surely! We would have given every person his guidance, but the Word from Me took effect that I will fill Hell with jinn and mankind together.
Here, Allah informs mankind that if He had willed, He could have given guidance to every person (without anyone having to choose it on his own). However, this was against His wisdom, since He wanted man to accept faith (Imaan) on his own, willingly and voluntarily, without being forced or compelled to do so. Allah says that His word had already become established and fixed, that He will fill Hell with sinners and disbelievers from among jinn and men. Hence, people will be given the choice to accept true faith or reject it. Those who accept it will be from among the believers who will be granted gardens in Paradise. As for those who reject faith, they will be cast into the fire of Hell and will be punished severely. This is Allah’s promise, and it will come to pass. (Safwatut Tafseer, Vol.12, Pg.38, Darul Quran Al Kareem, Beirut)
With respect to those who have chosen disbelief instead of belief, Allah says:
فَذُوقُوا بِمَا نَسِيتُمْ لِقَاءَ يَوْمِكُمْ هَٰذَا إِنَّا نَسِينَاكُمْ ۖ وَذُوقُوا عَذَابَ الْخُلْدِ بِمَا كُنْتُمْ تَعْمَلُونَ
14. Then taste you (the torment of the Fire) because of your forgetting the Meeting of this Day of yours, (and) surely! We too will forget you, so taste you the abiding torment for what you used to do.
In an admonishing and rebuking manner, the unbelievers will be told to taste the punishment of the Hellfire which they will receive on account of their denial of the hereafter. They were so caught up in the worldly life that they totally forgot that they will eventually meet Allah. On account of this, Allah will say to them, ‘Surely, We too will forget you’. It means that Allah will leave them to suffer in the punishment of Hell just as they left off faith (Imaan) and good deeds in the world. No compassion, mercy or kindness will be shown to them, and they will be ordered to suffer in the everlasting punishment for their disbelief and denial. Allah will say to them, ‘Taste the eternal punishment for what you used to do’.
Having mentioned about the unbelievers and their miserable state in the hereafter in the previous verses, Sura Sajdah goes further to mention the believers, as well as the great blessings Allah has kept for them in the hereafter. Regarding the true believers, Allah says in verse 15:
إِنَّمَا يُؤْمِنُ بِآيَاتِنَا الَّذِينَ إِذَا ذُكِّرُوا بِهَا خَرُّوا سُجَّدًا وَسَبَّحُوا بِحَمْدِ رَبِّهِمْ وَهُمْ لَا يَسْتَكْبِرُونَ
15. Only those believe in Our Ayât (proofs, evidences, verses, lessons, signs, revelations, etc.), who, when they are reminded of them fall down prostrate, and glorify the Praises of their Lord, and they are not proud.
Here, Allah mentions an outstanding quality of the true believers, and states that they are those who, when reminded (through the verses of the Holy Quran), fall on their foreheads, prostrating to Allah out of great respect for the verses of the Quran and out of fear for His punishment.
While in Sajdah (prostration), they (the believers) glorify and praise Allah excessively by saying, ‘Subhaanallahi wa bihamdihi’ or ‘Subhaana Rabiyal A’laa wa bihamdihi’ and other similar statements. These believers are not proud and haughty, and they do not have pride, conceit and arrogance. Instead, their hearts are filled with humility and the love for Allah. On account of this, they submit themselves to the obedience of Allah and turn to His worship.