If you believe that submitting to Allah is the truth but ignore it and you didn't follow it then yep. That's the biggest bad deed there is, by not acknowledging Allah as the true God. But no one knows their destiny.
On the authority of Abdullah bin Masud, who said: the Messenger of Allah, and he is the truthful, the believed narrated to us :
"Verily the creation of each one of you is brought together in his mother's belly for forty days in the form of seed, then he is a clot of blood for a like period, then a morsel of flesh for a like period, then there is sent to him the angel who blows the breath of life into him and who is commanded about four matters: to write down his means of livelihood, his life span, his actions, and whether happy or unhappy. By Allah, other than Whom there is no god, verily one of you behaves like the people of Paradise until there is but an arm's length between him and it, and that which has been written over takes him and so he behaves like the people of Hell-fire and thus he enters it; and one of you behaves like the people of Hell-fire until there is but an arm's length between him and it, and that which has been written over takes him and so he behaves like the people of Paradise and thus he enters it." related by Bukhari and Muslim
On the authority of Abu Hurairah, who said: the Messenger of Allah said :
p "Allah the Almighty is good and accepts only that which is good. Allah has commanded the faithful to do that which he commanded the messengers, and the Almighty has said: "O ye messengers ! Eat of the good things and do right". And Allah the Almighty has said : "O ye who believe! Eat of the good things wherewith We have provided you"
Then he mentioned [the case of] a man who, having journeyed far, is disheveled and dusty and who spreads out his hands to the sky [saying] : "O Lord! O Lord!" - while his food is unlawful, his drink unlawful, his clothing unlawful, and he is nourished unlawfully, so how can he be answered!" related by Muslim
On the authority of Anas, who said: I heard the Messenger of Allah say:
Allah the Almighty has said: "O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you. O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great as its." related by Al-Tirmithi, who said that it was a good and sound Hadith.
