The Messenger of Allah (sal Allahu alaihi wa sallam) said: “Temptations are presented to the heart, one by one. Any heart that accepts them will be left with a black stain, but any heart that rejects them will be left with a mark of purity, so that hearts are of two types: a dark heart that has turned away and become like an overturned vessel, and a pure heart that will never be harmed by temptation for as long as the earth and the heavens exist. The dark heart only recognizes good and denounces evil when this suits its desires and whims.” [Muslim, Kitab al-Iman]
Acts of obedience are essential to the well being of the heart of the servant of Allah, just in the same way that food and drink are to that of the body. All wrong actions are the same as poisonous foods, and they inevitably harm the heart.
The well being of the servant of Allah’s heart, however, is far more important than that of his body, for while the well being of his body enables him to lead a life that is free from illnesses in this world, that of the heart ensures him both a fortunate life in this world and eternal bliss in the next.
Giving in to temptations and disobeying Allah (subhana wa ta’ala) poison the heart and cause its sickness and ruin. Like an overturned bowl cannot hold any water in it, an overturned heart cannot hold any Iman in it.
Refusing temptations, on the other hand, polish and illuminate the heart, filling it with Iman and making it more beloved to Allah (subhana wa ta’ala).