What is Sealing of hearts?

Qadar in Terms of Sealing of Hearts
Allah addresses the Prophet (Peace be Upon Him) as follows in the Quran:
“As to those who reject Faith, it is the same to them whether thou warn them or do not warn them they will not believe. Allah hath set a seal on their hearts and on their hearing. And on their eyes is a veil; great is the penalty they (incur).” (al-Baqara, 2/6-7)
Some people who consider this verse superficially say, “Allah has set a seal on their hearts and on their hearing; He has put a veil on their eyes. How can they believe and worship? How can they see the truth and hear it?” However, for a person who considers the issue in terms of pre-eternity of Allah and the rule, ‘Knowledge is dependent on the thing known’, such a claim is groundless.
First of all, in the verse, the deed of denying is attributed to people and the deeds of setting a seal and putting a veil are attributed to Allah. That is, man himself prefers denying and insists on it; consequently, Allah sets a seal on his heart.
The fact that after the phrase “la-yu’minun”, which means “they do not believe”, comes the verb “khatama”, which means “set a seal”, shows clearly the reason why the heart is sealed. That is, they did not believe; so, their hearts were sealed as a punishment.
As it is known, regarding voluntary deeds, the universal will of Allah Almighty is dependent on the partial free will of man. That is, Allah creates whatever man wants to be created. Here, people prefer denying; and as a result of their denial, Allah seals their hearts and ears. We can understand this truth through the following example:
Suppose that municipal policemen are inspecting the bakeries and checking whether the bakeries are producing healthy food or not. After the municipal policemen inspect several clean and legitimate bakeries, they come across a bakery which is very dirty, which is full of insects and which produce food in unsanitary conditions. What the municipal policemen are to do there is to close down and seal this bakery, which produces food in bad conditions.
When the municipal policemen seal the bakery, can the owner of the bakery say, “The municipal policemen sealed my bakery; I cannot produce food because of their fault.” Definitely not. Yes, the municipal policemen sealed the bakery; it is true, but he himself did the things that caused the bakery to be sealed. He did not clean the bakery and he did not act in accordance with the rules of hygiene. That is, the act of sealing by the municipal policemen originates from the low ethics of the owner of the bakery. If he had kept the bakery clean, it would not have been sealed. The municipal policemen do not have a grudge against bakers because many bakeries continue producing food; they are not sealed.
In brief, the military policemen sealed the bakery but the owner of the bakery is to be blamed.
Similarly, if man, who is like the baker in the metaphor, does not keep his heart, which is like the bakery in the metaphor, clean from polytheism, sins, disobedience and so on, Allah will seal his bakery, which is his heart. Bread cannot be produced in a sealed bakery; similarly, virtues like belief, love and knowledge of Allah, cannot exist in a sealed heart.
Allah Almighty’s endless bounties and grants that He displays in man and in the universe are seen through the light of belief. Sins, rebellion and especially unbelief veil those bounties and grants. As man keeps committing sins and rebellion, the veil between him and his Lord gets thicker.
If a person does not repent of the sins he has committed and does not transform his shame into peace, through the enforcement of his soul, pride, hypocrisy, lust and eventually unbelief settle in his heart instead of the light of belief. This state makes him blind and consequently causes his heart to be sealed.
Otherwise, Allah does not seal the heart of a person who has belief and does good deeds. That is, the people who are in the way of unbelief do not read the numerous proofs that witness the existence and oneness of Allah, His mercy and generosity; and they do not hear the endless voices and sounds; thus, they themselves cause their hearts and ears to be sealed and their eyes to be veiled.
When the question, “How will a person find guidance after his heart is sealed?” is viewed under the light of the rule, “Knowledge is dependent on the thing known”, the following result will be seen: Since Allah Almighty knew through His pre-eternal knowledge that they would choose unbelief and that they would use their partial free will in the way of polytheism and unbelief, He sealed their hearts through His universal will. If they had used their partial free will in the way of guidance, Allah would definitely not have sealed their hearts with His universal will and would have opened ways of guidance for them. Regarding voluntary deeds, Allah Almighty’s universal will is dependent on man’s partial free will.
Here, the sentence, “They will not believe” is a determination that is based on scientific knowledge. That is, Allah’s pre-eternal knowledge knew that they would not believe in the future, either; so, He sealed their hearts. It does not mean that even if they want to believe using their wills, they cannot believe. The sentence, “They will not believe” is stated because it is known that they will not believe. Their will was not removed and they were not condemned to unbelief. As it was stated before, the attribute of knowledge is not stringent.
On the other hand, the verse mentioned above was sent down about the polytheists who opposed and struggled against the Messenger of Allah. The full dominance of polytheism over the hearts of the polytheists and leaving no room to oneness is expressed as “sealing of the heart”. Those whose door of guidance is closed are the polytheists who are in that position. The door of guidance is not closed for everybody that commits sins, that oppresses people or commits polytheism. Otherwise, how can we explain the fact that the Prophet (Peace be Upon Him) continued to convey the message of Islam and that tens of thousands of people who previously worshipped idols became Muslims? If the heart of every polytheist had been sealed, no polytheist would have embraced Islam. That is, those whose hearts are sealed are the people who cannot accept oneness. They fall into this hole by using their will in a wrong way.