It is a matter of concern whether God seals/locks people’s hearts, and if He does, how people can be held responsible for it. Let us take a look at the related verses.
The Almighty God decrees:
خَتَمَ اللَّهُ عَلَى قُلُوبِهِمْ وَعَلَى سَمْعِهِمْ وَعَلَى أَبْصَارِهِمْ غِشَاوَةٌ وَلَهُمْ عَذَابٌ عَظِيمٌ.
“(It is as if) God has sealed their hearts and their hearing; and their vision is veiled. There is a great chastisement for them.” (Al-Baqarah/The Bull; 2:7)
In this verse, bad consequences of bad behaviors are expressed using metaphors. A metaphor is defined as, ‘a figure of speech in which a term or phrase is applied to something to which it is not literally applicable in order to suggest a resemblance’. For example, a person who says: “He is such a fox!” does not actually talk about a fox, but he likens a man to a fox without using a preposition of similarity.
Metaphors in figurative language can also be used to create a scene in reader’s mind, and let them gain new insights into the objects or subjects in the work. “He was a gentle lamb to the slaughter.” or “All the world’s a stage!” are examples of figurative language because, it is not possible to mean the literal meaning of the sentences, and preposition of similarity is not used.
Figurative language is also used in the verse above, to represent the prejudiced attitude of ignorers against Qur’an. In figurative language, the literal meaning cannot be meant; so is in this verse. Otherwise, these people could not be held responsible. Someone whose heart and hearing is sealed, and whose vision is veiled would not be responsible for believing in anything. Yet, God the Almighty decrees:
“Allah does not impose upon anybody a duty but to the extent of its ability.” (Al-Baqarah/The Bull; 2:286)
Since these sentences are wrongly assumed to express their literal meanings rather than metaphoric ones, disclosing the implicit “as if” in the sentences becomes obligatory.
It is the same for the following verses of Chapter Ya-Sin:
لَقَدْ حَقَّ الْقَوْلُ عَلَى أَكْثَرِهِمْ فَهُمْ لَا يُؤْمِنُونَ . إِنَّا جَعَلْنَا فِي أَعْنَاقِهِمْ أَغْلَالًا فَهِيَ إِلَى الْأَذْقَانِ فَهُمْ مُقْمَحُونَ . وَجَعَلْنَا مِنْ بَيْنِ أَيْدِيهِمْ سَدًّا وَمِنْ خَلْفِهِمْ سَدًّا فَأَغْشَيْنَاهُمْ فَهُمْ لَا يُبْصِرُونَ . وَسَوَاءٌ عَلَيْهِمْ أَأَنْذَرْتَهُمْ أَمْ لَمْ تُنْذِرْهُمْ لَا يُؤْمِنُونَ
“Most of them have realized the Word (that it is from God), but they do not believe. As if We placed shackles around their necks, up to their chins, so their heads remain facing upwards. And We placed a barrier in front of them, and a barrier behind them, and We have enshrouded them, so they cannot see. It is the same for them, whether you warn them, or do not warn them; they do not believe.” (Ya-Sin; 36:7-10)