From An Explanation of Riyaadh as-Saaliheen:
The servant is not afflicted with a punishment greater in severity than the hardening of the heart and its being distant from Allaah. The Fire was created to melt the hardened heart, this heart which is the most distant of hearts from Allaah. If the heart becomes hardened the eye becomes dry. …
The heart becomes sick as the body becomes sick and its cure lies in repentance and seeking protection from evil.
It becomes rusty as a mirror becomes rusty and it is polished through dhikr.
It becomes naked as the body becomes naked and its adornment comes about through taqwaa.
It becomes hungry and thirsty as the body becomes hungry and thirsty and its hunger and thirst is satiated through knowledge, love, reliance, repentance and servitude to Allaah.
From: http://www.troid.org/raqaaiq/strengthening-the-heart/the-hardness-of-the-heart.html Al-Fawaa`id [pp. 111-112] of ibn Qayyim al-Jawziyyah, may Allaah have mercy upon him. [The translation is taken from ‘An Explanation of Riyaadh as-Saaliheen Vol. 1, Trans. Abu Sulaymaan and modified.]
-may Allah ta’ala reward the person who sent this to me abundantly, Ameen.
«لا إله إلا الله ولا نعبد إلا إياه، له النعمة وله الفضل وله الثناء الحسن، لا إله إلا الله مخلصين له الدين ولو كره الكافرون»