قَدْ أَفْلَحَ مَن زَكَّاهَا وَقَدْ خَابَ مَن دَسَّاهَا

He has succeeded who purifies it, and he has failed
who instills it [with corruption].
(Quran, 91:9-10)

True success depends upon a pure heart, in which there is love for Allah and also fear of Allah. Our hearts get sick due to our indulgence in this world and so we need to purify them.