Explaining the importance of obedience, avoidance of sins and repentance for the preservation of īmān, Imām al-Ghazālī writes:
Īmān is not one door but is over seventy doors, the highest of them the testimony that there is no deity but Allāh and the lowest of them removing harm from the road. An example of this is someone saying: “The human being is not one entity, but is over seventy entities, the highest of them is the heart and soul and the lowest of them is removing offensive things from the skin in that one has a trimmed moustache, clipped nails, and skin free of filth, so that he is distinguished from unrestrained beasts soiled in their faeces with offensive forms owing to their lengthy talons and hooves.”
This is a fitting example for īmān is like a human being. Losing the testimony of Tawḥīd entails complete negation just like losing the soul. The one who does not have [anything] besides the testimony of Tawḥīd and Risālah is like a person with amputated limbs, gouged-out eyes, missing all external and internal parts besides the essence of the soul. Just as the one whose condition is such is close to dying – the weak and isolated soul, from which the parts that assist and strengthen it have fallen behind, parting from him – similarly, the one who does not have [anything] besides the essence of īmān and falls short in actions comes close to the tree of his īmān being uprooted when strong winds that shake the īmān strike it at the initial arrival and coming of the Angel of Death. Every īmān whose roots are not established within certainty and whose branches are not spread out within actions will not remain firm in [the face of] the torrents of horrors when the head of the Angel of Death appears. Sū’ al-khātimah (an evil end) will be feared for him, unless he is watered with acts of obedience with the succession of days and hours so that [his tree of īmān] becomes firmly-rooted and strong.
The sinner who says to an obedient individual: “I am a believer just as you are a believer”, is like the gourd plant saying to the stone pine: “I am a tree and you are a tree.” How wonderful is the reply of the stone pine when it says: “You will realise that you are deluded by sharing the same name when the autumn winds blow – upon which your roots will be uprooted and your leaves scattered, and your delusion in sharing the name ‘tree’ while being ignorant of the causes of trees being firmly-rooted will be exposed.”
Soon you will see when the dust appears
Is it a steed beneath you or a donkey
This is something that will manifest at death. The atrium of the knowers [of Allāh] is cut with fear of the tragedies of death and its horrifying precursors, upon which very few are firm.
The sinner who does not fear eternity in the Fire because of his sins is like a healthy person engrossed in desires that are harmful to the body not fearing death because of his good health and [the fact] that death does not normally occur suddenly. It will be said to him: “The healthy person fears sickness and then when he becomes sick he fears death.” So too the sinner – he fears sū’ al-khātimah, and then when his end is evil (Allāh forbid!), eternity in the Fire is necessary. Sins to īmān is like harmful foods to the body. It continues to assemble within and alter the temperament of the humours without one realising until the temperament becomes corrupt, and then he falls ill suddenly and then dies suddenly – and the same is the case with sins.
If the one who fears death in this temporary world must abandon poisons and harmful foods in all cases and with immediate effect, the one who fears eternal destruction has a greater obligation to do this. If the consumer of poison, when he feels remorse, must throw up and turn back from consuming it and take it out of his stomach immediately and without delay to restore his body that has come close to a perishing that will only make him lose this temporary world, then the consumer of the poisons of Dīn – that is, sins – has a greater obligation to turn back from them with every possible rectification so long as there is opportunity for rectification – and that is life. That which is feared from this poison is losing the eternal afterlife in which there is eternal bliss and a great kingdom, and in losing it there is Hellfire and eternal punishment, against one percent of the duration of which many times the lifetimes of this world would wane, because its duration has no end at all. So, rush towards repentance before the poisons of sins have taken such effect on the soul that it is beyond the control of doctors… (Iḥyā’ ‘Ulūm al-Dīn, Dār al-Minhāj, 7:29-31)