Man is intrinsically selfish; he is extremely sensitive about issues linked to his own interests. Ironically, he displays indifference towards death, which ought to be a matter of paramount concern. In the Qur'an, this state of mind peculiar to "those who do not hold firmly to Faith" is defined by God in one word: "heedlessness".
The meaning of heedlessness is a deficiency in full comprehension of facts owing to a blurring of awareness or even total unawareness and the resultant failure to arrive at sound judgments and give pertinent responses. An example of this is given in the following verse:
Mankind's Reckoning has drawn very close to them, yet they heedlessly turn away. (Surat al-Anbiya': 1)
People feel certain that one who is afflicted by a fatal or incurable disease will die. Yet, no less than this patient, these people who harbor such feelings of certainty, too, will die. That this will happen some time in the future or very soon does not change this fact. Often, heedlessness obscures this truth. For instance, it is highly probable that someone afflicted with HIV will die in the near future. Yet, the fact remains that it is also highly probable -if the truth be told, it is certain-that a vigorous person next to him will one day die. Maybe death will come upon him long before it comes upon that "HIV-stricken patient." This will most likely be at some quite unexpected moment.
Death, especially at an early age, seldom comes to mind. Considering this as the end, man even escapes from the thought of it. However, just as physical avoidance provides no cure for death; neither does avoidance of thinking about it. Besides, it is impossible to ignore death. Every day, newspapers run headlines about the deaths of so many people. You frequently come across hearses or pass by cemeteries. Relatives and associates die. Their funerals or visits to offer condolences inevitably bring death to mind. As one witnesses the death of others, and especially the death of beloved ones, he inevitably thinks about his own end. This thought hurts him deep inside, making him restless.
No matter how strongly the individual resists, wherever he seeks refuge or how he tries to escape, he may actually encounter his own death at any moment. He has no other choice. Ahead of him, there is no other exit. The countdown never stops, not for a moment. Wherever he returns,
death meets him there. The circle encloses constantly and finally catches up with him:
Say: 'Death, from which you are fleeing, will certainly catch up with you. Then you will be returned to the Knower of the Unseen and the Visible and He will inform you about what you did.' (Surat al-Jumu'ah: 8)
Wherever you are, death will catch up with you, even if you are in impregnable fortresses. (Surat an-Nisa': 78)
That is why we need to stop deceiving ourselves or disregarding facts and strive to earn the good pleasure of God during this period predetermined by Him. Only God knows when this time will be over.
Our Prophet Mohammad (pbuh) also said that one of the best ways to prevent one's conscience from hardening, and attain a good character is by frequently remembering death:
Abdullah ibn Umar narrated, "Gods's Messenger (peace be upon him) said, 'These hearts become rusty just as iron does when water affects it.' On being asked what could clear them he replied, 'A great amount of remembrance of death and recitation of the Qur'an.'" (Al-Tirmidhi, 673)