That some people cannot understand the Qur'an is one of the most important secrets revealed in the Qur'an. This is indeed an important secret, because the Qur'an is a very clear, easy and straightforward book. Anyone who wishes can read the Qur'an and learn about God's commands, the good morals that He is pleased with, the attributes of paradise and hell, and about many secrets some of which are presented in this guide. However, as an immutable law of God, some people cannot understand the Qur'an despite all its clarity. Furthermore, these people can be atomic engineers or professors of biology, can understand very complicated branches of science such as physics, chemistry or mathematics, can grasp Buddhism, Hinduism, Shintoism, materialism or communism, and yet fail to understand the Qur'an. These people who adopt the complicated structures of non-Qur'anic systems somehow cannot grasp God's clear and easy religion, and fail to understand even the most evident subjects therein.
Their being unable to grasp even the most evident facts is a miracle in itself. By showing that they have such a serious deficiency in understanding, God explains that some people possess a different nature. On the other hand, this provides evidence to the fact that all hearts, reason and comprehension is in God's hands. God declares that He will cover the hearts and comprehension of those who are seized by feelings of grandeur, that is who do not submit to God. The fact that they understand anything but the Qur'an reveals that God has diverted them from His signs, and they are debarred from the Qur'an because of their insincerity. Some of the verses pertaining to this are:
When you recite the Qur'an, We place an obscuring veil between you and those who do not believe in the hereafter. We have placed covers on their hearts, preventing them from understanding it, and heaviness in their ears. When you mention your Lord alone in the Qur'an, they turn their backs and run away.
Some of them listen to you but We have placed covers on their hearts, preventing them from understanding it, and heaviness in their ears. Though they see every Sign, they still have no faith, so that when they come to you, disputing with you, those who are disbelievers say, 'This is nothing but the myths of previous peoples!'
Who could do greater wrong than someone who is reminded of the Signs of his Lord and then turns away from them, forgetting all that he has done before? We have placed covers on their hearts, preventing them from understanding it, and heaviness in their ears. Though you call them to guidance, they will nonetheless never be guided.
As revealed in the verses, the secret why disbelievers cannot understand the Qur'an is that God has placed a barrier to their comprehension and set a seal upon their hearts because of their denial. This is a great miracle displaying the grandeur of God and that He is the possessor of hearts and thoughts of every man.
