Shamsuddeen Muhammad bin Abee Bakr Ibn Qayyim al-Jawziyyah [D.751 A.H.] [رحمه الله] said: There is no doubt that the heart becomes rusty just like brass and silver and other things become rusty, and it becomes bright and illuminated with Dhikr. It becomes so bright until it is a shiny mirror, therefore if the heart is left then it becomes rusty and if it remembers Allaah it becomes illuminated. The heart becomes rusty due to two matters: 1- negligence 2- sins