In order not to feel regret in the hereafter

Why should Allah punish you if you are thankful and have faith? Allah is All-Thankful, All-Knowing. (Surat an-Nisa:147)

People are created with many weaknesses and imperfections. Throughout our lives, we forget many things and make countless mistakes. However through repentance, which Allah grants us as a great favor, it is always possible in this world to correct our mistakes. Indeed, the world is created just for this purpose: we are trained, put to test, and purified of our mistakes in this world. It is likely that we may deeply regret our mistakes or the way we have led our lives. However, it is always possible to make up for this regret. After having lived through this regret, we can ask for repentance and hope for Allah's forgiveness.In the Qur'an, Allah gives the glad tidings that He will forgive any sin provided one repents sincerely. Allah knows our inner thoughts and every word we keep to ourselves. He knows whether we are true to Him or not. Allah, in the Qur'an, describes His closeness to his servants:
 

Your Lord knows best what is in your selves. If you are righteous, He is Ever-Forgiving to the remorseful. (Surat al-Isra: 25)

Yet, another important fact surfaces here; after death, it is not possible to make up for the mistakes and sins committed in this world unless Allah wills otherwise. So not a single moment do we have to lose. Minutes pass by in a blink of the eye and with every moment passing, we draw even closer to death. Furthermore, we can never foresee when death will confront us. Its date, hour and minute can never be known. We all will certainly die one day and will give an account of our deeds in the presence of Allah.

For this reason, man must always bear in mind that he may soon die. If he is not to regret in the Hereafter, he must reconsider his life.

If it were the time to meet the angels of death right now, would you be able to give an account of all the years you have spent in this world?

What have you done so far to earn the consent of Allah?

Have you been meticulous enough in fulfilling Allah's commands?

A person might not have an affirmative answer to any of these questions. But if he repents and sincerely makes an absolute commitment to live to earn the good pleasure of Allah, then he can hope for Allah's forgiveness. The Messenger of Allah (saas) frequently sought forgiveness from Allah:

By Allah, I seek the pardon of Allah and return penitently to Him every day more than seventy times. (Bukhari)

We must take refuge in Allah, Who is al-Ghaffar (The Forgiver, He Who is All-Forgiving), al-Halim (Forbearing One, He Who is clement), and al-Tawwab (The Acceptor of repentance). Allah will absolutely give the rewards of those who persevere and often turn to Him. He will certainly forgive His servants who have faith and reward their good deeds according to the best of what they did. In one verse, Allah states this great glad tiding as follows:

What is with you runs out but what is with Allah goes on forever. Those who were steadfast will be recompensed according to the best of what they did. Anyone who acts rightly, male or female, being a believer, We will give them a good life and We will recompense them according to the best of what they did. (Surat an-Nahl: 96-97)

Allah's Messenger (saas) also called on believers to be steadfast in doing good deeds and gave them the good news that they will be rewarded by Allah if they do so:
 

The Prophet (saas) said,"Carry on doing (good deeds), for everybody will find it easy to do (what will lead him to his destined place)." Then he recited "As for him who gives (in charity) and keeps his duty to Allah, and believes in the best reward from Allah (i.e. Allah will compensate him for what he will spend in Allah's way). So, We will make smooth for him the path of ease. But he who is a greedy miser...for him, the path for evil." (Bukhari)

Never forget that at any time any one of us might be caught by death and, though being full of regret, might not have again the opportunity to correct the wrongs we committed in the worldly life. For this reason, we should lose no time in asking for repentance from Allah and living by His commands and the sunnah of the Prophet (saas). This is the only way to be a servant upon whom Allah bestows His mercy and love. This is again the only way to attain Paradise, the eternal abode Allah prepares for His true believers.