Have you seen those who wear the outfit of a scientist, who speak of science, of ideas, of philosophy and social reforms, who mislead thousands or millions of people, yet they are doing that just for a salary, for financial favors, or perhaps the status that they enjoy. It is the salary or some money given to such people which motivates them. They are so much connected with money and position to the extent that the truth does not matter anymore.
Have you ever seen those who have a political or social position, who lead people and mislead them, who speak in the name of people, whose very lives are inseparable from that image, to the extent that they become blind and slaves of their own persona - do you think they are going to change their mind if the truth is clarified to them? Do you think they are ready to give up what they have for the sake of the truth?
Have you seen those who are famous, who live for fame, whose lives revolve around it, who, ironically, are turned into slaves of it, who benefit from it, who enjoy it and their fame is everything for them - do you think they are ready to give it up for the truth?
Have you seen the one who has spent the whole life studying in Secularist schools, which are filled with disinformation, lies, propaganda, whose curricula are based on purely political agendas - not pure science, who have been exposed to that type of knowledge from a young age and graduate, perhaps with honors, and then get a good job because of that certificate - do you think such a person is ready to accept the truth if it contradicts his or her education and preconceived notions?
Have you seen those who stick to an idea, who continue living a certain life, who argue, who think they are upon something, who even feel some sense of life accomplishment, yet they are doing that perhaps for some mediocre or ordinary reasons - for money, for a job, for a house, for a woman, or perhaps they are afraid of facing negative consequences should they lose any of those? So, there is no great reason behind them, no belief, no conviction, and no certainty even if they appear acting upon a great cause.
Such are some of the examples of what the Qur'an refers to as the locks of heart, which prevent people from understanding the truth, from reflecting and pondering over the Qur'an, which says,
"Do they not then reflect on the Quran? Or are there locks upon their hearts?" [47:24]
In other words, the Qur'an is saying that there are impediments to the understanding of the Qur'an, which are called locks.
The Qur'an has been revealed to the Prophet Muhammad (peace be upon him) in clear and plain Arabic as a guidance for humanity and in order to reflect on its meanings, yet people fail to understand it, not because the Qur'an is not clear and eloquent, but the hearts are locked according to the Qur'an itself; they are prevented by preconceived notions, arrogance, money and position etc.