In another verse, it is stated:

اَ لَّذِیۡ    خَلَقَ   الۡمَوۡتَ   وَ الۡحَیٰوۃَ    لِیَبۡلُوَکُمۡ    اَ یُّکُمۡ    اَحۡسَنُ   عَمَلًا ؕ

Translation from Kanz-ul-Iman: The One Who created death and life to test you - who among you has the better deeds. (Part 29, Surah Al-Mulk, verse 2)

Just ponder, the purpose of our life is to worship Allah عَزَّوَجَلَّ and to abundantly perform good deeds, but hard-heartedness is a disease which makes a person forget even his purpose of life.

Third harmful effect

Another harmful effect of hard-heartedness is that due to its evil effects, the previous good deeds go to waste. The Holy Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم said: Six things ruin a deed: (1) the act of finding faults with people (2) Hard-Heartedness (3) Love for the world (4) Lack of shame (5) high hopes (6) Oppression beyond limits. (Kanz-ul-‘Ummal, vol. 8, pp. 36, Hadees 44016)

Fourth harmful effect

Another curse of hard-heartedness is that a person becomes deserving of Allah’s displeasure and curse (i.e., that person is far away from the mercy of Allah عَزَّوَجَلَّ). Sayyiduna ‘Ali رَضِىَ اللهُ تَعَالٰی عَـنْهُ has narrated that the Beloved Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم said: Ask for goodness from the kind-hearted people of my Ummah. Stay close to them and do not ask for goodness from hard-hearted people because curse descends upon them.

(Al-Mustadrak, vol. 5, pp. 458, Hadees 7978)

یا رَبّ پئے رضا مجھے وہ آنکھ دےکہ جو

عشقِ رسول ِ پاک میں آنسو بہا سکے

وہ آگ میرے سینے میں آقا لگائیے

پتھر سے سخت دل کو بھی جو کہ جلا سکے