In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah [The Exalted] said:
وَمَا يَسْتَوِي الْأَعْمَىٰ وَالْبَصِيرُ
وَلَا الظُّلُمَاتُ وَلَا النُّورُ
وَلَا الظِّلُّ وَلَا الْحَرُورُ
وَمَا يَسْتَوِي الْأَحْيَاءُ وَلَا الْأَمْوَاتُ ۚ إِنَّ اللَّهَ يُسْمِعُ مَن يَشَاءُ ۖ وَمَا أَنتَ بِمُسْمِعٍ مَّن فِي الْقُبُورِ
إِنْ أَنتَ إِلَّا نَذِيرٌ
إِنَّا أَرْسَلْنَاكَ بِالْحَقِّ بَشِيرًا وَنَذِيرًا ۚ وَإِن مِّنْ أُمَّةٍ إِلَّا خَلَا فِيهَا نَذِيرٌ
Not alike are the blind and the seeing. Nor are (alike) the darkness and the light. Nor are (alike) the shade and the sun’s heat. Nor are (alike) the living and the dead. Verily, Allah makes whom He will hear, but you cannot make hear those who are in graves. You (O Muhammad) are only a warner. Verily! We have sent you with the truth, a bearer of glad tidings, and a warner. And there never was a nation but a warner had passed among them. [Surah Al-Faatir. Aayaat 19-24]
Allaah [The Exalted] informed us that the opposites are not the same based on what His Wisdom necessitates and that which is placed in the sound natural disposition of His slaves.
[وَمَا يَسْتَوِي الْأَعْمَىٰ وَالْبَصِيرُ – Not alike are the blind and the seeing]-Meaning, just as it established in their midst – without any doubt – that these mentioned things are not equal (or are not the same), then likewise they should know that the opposites (related to beliefs, acts of worship, deeds) are even more so not the same. Neither are the believer and the disbeliever the same nor are the guided one and the misguided one the same. Neither is the knowledgeable person the same as the ignorant one nor are the inhabitants of paradise and hell the same. Neither are those whose hearts are dead (due to disbelief) the same as those whose hearts are alive (due to Eemaan). There is a (huge) difference between these things of that which none knows besides Allaah. So, if one knows their different statuses, makes a distinction between the affairs and it becomes clear regarding the affair that is obligated on you to compete one another and attain, as opposed to its opposite, then the determined one would choose for himself that which is more worthy and has more right to be given precedence.
[ إِنَّ اللَّهَ يُسْمِعُ مَن يَشَاءُ – Verily, Allah makes whom He will hear]- Meaning, the hearing (that leads to sound) understanding and acceptance of truth, because indeed Allaah is the guide and the one who bestows guidance.
[ وَمَا أَنتَ بِمُسْمِعٍ مَّن فِي الْقُبُورِ- But you cannot make hear those who are in graves] – Meaning, those whose hearts are dead (due to disbelief, wicked deeds etc); or just as your supplication cannot benefit the inhabitants of the graves in anything (except by the will of Allaah), likewise it does not benefit the one who turns away – the stubborn one – in anything (except by the will of Allaah), but your job is to warn and propagate what you are sent for, whether it is accepted from you or not. This is why Allaah said:
إِنْ أَنتَ إِلَّا نَذِيرٌ
إِنَّا أَرْسَلْنَاكَ بِالْحَقِّ
You [O Muhammad] are only a wamer. Verily! We have sent you with the truth).
Meaning, We only sent you with the truth, because indeed Allaah sent you after a period in which there were no Messengers when people deviated from the right path and were deprived of knowledge, and there was a great need to send you. So, Allaah sent you as a mercy to the creation. Likewise, the upright religion and the straight path with which We sent you is truth and not false, and likewise this great Qur’aan with which We have sent you – which gathers the wise reminder – is the (only) Haqq [i.e. truth that addresses the real state of affairs and there is no way of rejecting it] and it is Sidq [i.e. the only truth that passes perfect and infallible judgement on the real state of affairs].
You (O Muhammad) are a warner- Meaning, you convey glad tidings of Allaah’s reward in this life and the next for the one who obeys you, and a warner to the one who disobeys you regarding Allaah’s punishment in this life and the next, and you are not a new thing amongst the Messengers, because [وَإِن مِّنْ أُمَّةٍ إِلَّا خَلَا فِيهَا نَذِيرٌ- And there never was a nation but a warner had passed among them]- Meaning, the previous nations and generations. Allaah’s proofs were established on them, [لِّيَهْلِكَ مَنْ هَلَكَ عَن بَيِّنَةٍ وَيَحْيَىٰ مَنْ حَيَّ عَن بَيِّنَةٍ- So that those who were to be destroyed (for their rejecting the Faith) might be destroyed after a clear evidence, and those who were to live (i.e. believers) might live after a clear evidence. (Surah Al-Anfaal. Aayah 42)]
An Excerpt from Tafseer As-Sadi. Slightly paraphrased