Imaam Ibn al-Qayyim writes in his al-Fawaa-id:
Just as when the body is ill and food and drink do not serve their normal purpose, when the heart is ill with the temptations of unlawful desires, advice and counselling give no benefit.
He who wishes for the purity of his heart should give preference to the commands of Allah over his own desires.
He who keeps his heart near Allah will find peace and tranquillity, whilst he who gives his heart to the people will find restlessness and apprehension.
The heart becomes ill just like the body becomes ill; its cure is in repentance and opposing the desires. It becomes rusted just like a mirror; its polish is in the remembrance of Allah. It is naked, but clothed through taqwa (piety). It becomes hungry and thirsty like the body; its nourishment is in the recognition and love of Allah and in the reliance and servitude towards Him.