Shaykh Al-Uthaymeen – Rahimahullaah – said:
Among the causes of decrease in imaan is ignorance concerning Allah The Most High. (Ignorance) of His names and attributes, as well as inattention and disregard towards contemplating over His universal and legislative laws. For indeed that is what results in (either) sickness of the heart or it’s death, due to doubts and desires overwhelming it (i.e. the heart). Likewise perpetrating sins decreases one’s imaan, in accordance to the type of sin commited, the degree of the sin, laxity concerning it, as well as the strength or weakness of the factors that invite one to it.
فتح رب البرية بتلخيص الحموية / ص105
Translated by Abu Arwah Ali bin Mushtaq Mir