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.