The most abhorrent sin is blasphemy, regardless of the kind of blasphemy. This is the sin which Allah will not forgive if the person dies without repenting of it.
If the person dies as a blasphemer, he will go to Hellfire and remain in it forever, even if he treated the people in a good manner, even if he gave a lot of charity to the poor. He will end up in hellfire and be tortured in it forever.
Allah ta^ala said “Innal-ladhina kafaruw wa sadduw ^an sabilillah, thumma matuw wa hum kuffar, falan yaghfirallahu lahum,” which means “Those who blaspheme, and they encourage others to blaspheme, and then they die on blasphemy, Allah will not forgive them.”
This is why a person has to endeavour to die as a Muslim. Because if a person dies as a Muslim, even if he died as an enormous sinner, if Allah does not forgive him, he will be tortured for a period of time for his sins, and then because of his belief, he will be taken out of hellfire and entered into Paradise.
Allah ta^ala told us in Al-Qur’an that Nabiyy Yusuf made a du^a and he said in his du^a a statement which means “O Allah, make me die as a Muslim.” We know that a prophet does not blaspheme, but this is to show us how important the matter of belief is. Also, Allah mentioned in Al-Qur’an that Nabiyy Ya^qub told his children to adhere to Islam and die as Muslims. This shows the importance of adhering to Al-Islam.
Al-Bukhariyy narrated that the Prophet, sallallahu ^alayhi wa sallam, that he said “Yakhruju minan-Nari man qala ‘La ilaha illallah’ wa fi qalbihi waznu dharratin min iman,” which means “The person who believes, even if his belief is weak, if he dies as Muslim, if he is tortured in Hellfire, he will not remain in it.” So a person has to protect his belief, and if he dies as a Muslim, this is what guarantees for him Paradise.
O Allah, make me die as a Muslim. (May Allah have mercy on those who say ameen).
