Is there any cure for a heart that has stopped feeling guilty of sins?
Perhaps reading about Hellfire and how serious it is, how He gave you all these blessings and you repaid Him with disobedience, or how so many people in their graves wish for Islam, and how you have that blessing and yet still sin, how repeating a minor sin makes it a major sin, so how serious is it to keep doing a major sin?
How Allaah never forgets what you do, thinking of all the people you hurt, how you were meant for better things than this but you failed yourself, how you forget how valuable you used to be, but you traded it for a sin, a short pleasure.
Or perhaps how the only sins you could have committed were with the same blessings He gave you, and yet He keeps answering your du’a and keeps giving you blessings despite how unworthy you have made yourself due to your sins.
Or maybe how people see you to be a good person and yet Allaah knows everything you did. How you fear having your secret sins revealed to people, but find peace in knowing that Allaah knows about them? How you sometimes laugh despite disobeying a God who is always there for you.
Staying awake at night and just reflecting on how your sins have encased your heart in darkness the same way you have encased yourself in a dark room.
But just remember it is better to feel guilt for your sins earlier than later, because once it becomes very late, you will become overwhelmed and find yourself in a position where you are tortured by the guilt every waking moment of your life and nothing you do will ever ease it. Guilt is an ocean that purifies us, but too much of it ruins a man..