Shaykh al-Islaam Ibn Taymiyyah (rahimahullah) said:
“Remembrance is to the heart what water is to the fish. And what is the state of a fish that leaves water?”
Ibn Qayyim al-Jawziyya (rahimahullah) said:
“Doubtless, a heart grows tarnished like brass or silver, and its polish is by remembrance, which may make it shine like a crystal mirror. So when one neglects the remembrance it tarnishes, and when he returns it shines. Since the heart is tarnished by two things- heedlessness and sin- it is polished by two things: remembrance and asking forgiveness.”
-Ibn Qayyim al-Jawziyya, The Invocation of God.