You should know that all acts of disobedience are poison to the heart and cause its sickness and ruin. They result in its will running off course, against that of Allah, and so its sickness festers and increases. Ibn Al-Mubarak said:
I have seen wrong actions killing hearts, and their degradation may lead to their becoming addicted to them. Turning away from wrong actions gives life to the hearts, and opposing yourself is best for it.
Whoever is concerned with the health and life of his heart, must rid it of the effects of such poisons, and then protect it by avoiding new ones. If he takes any by mistake, then he should hasten to wipe out their effect by turning in repentance and seeking forgiveness from Allah, as well as by doing good deeds that will wipe out his wrong actions.
By the four poisons we mean unnecessary talking, unrestrained glances, too much food and keeping bad company. Of all the poisons, these the most widespread and have the greatest effect on a heart’s well being.
Ibn Al-Qayyim said with regards to what one should do to cure his weak Iman using the Quran;
“First you should remove your heart from the life of this world and settle it in the Last Life. Then, pay your full attention to pursuing the meanings of the Quran, and try to comprehend and understand them and what they were sent down to accomplish. Then, offer these meanings to the sickness that your heart feels, and when they touch the disease, they will cure the heart, Allah willing.“
إن الله تعالى جعل رمضان مضمارا لخلقه ، يتسابقون فيه بطاعته إلى مرضاته ، فسبق قوم ففازوا ، وتخلف آخرون فخابوا ، فالعجب من الضاحك اللاعب في اليوم الذي يفوز فيه المحسنون ، ويخسر فيه المبطلون
“Indeed Allah has made Ramadan a means of gain for His creation. (Within this month) they race to gain His pleasure through obedience to Him. Some individuals will gain (win), while others will remain back and lose. It is amazing to see a person playing and laughing on a day that the good doers will be rewarded, and the wrong doers will be defeated.”