Weakness of Iman: Its Signs of Weakness, Causes and cure

The phenomenon of weak Iman has become very widespread among Muslims, and many people complain about the hardness of their hearts. So often we hear the words, 

'I feel hardness in my heart,'
'I do not find any joy in worship,'
'I feel that my faith has hit rock bottom,'
'Reading Quran does not move me,'
'I fall into sin easily.'

So the believer must check his heart, find out the nature and cause of the problem, and start treating it straight away, before it overwhelms him and destroys him. The matter is of utmost seriousness, for Allah has warned us against the heart that is hardened, closed, sick, blind and sealed.