And this is especially relevant in our times of the symptoms of a hard heart is to be selfish about yourself and not care about the rest of the Ummah. If you are disconnected from the reality of the Ummah. If you go to sleep at night and you couldn't care less about the massacre that just happened, villages after villages.
If you're not thanking Allah (subhana WA Ta'ala) for the blessings you have and you're disconnected from the reality of the Ummah and all you're worried about is your connection to your iPhone is not good in your particular classroom. You don't have the latest upgrade, computer. If your problems are clearly what is now called first world problems and you have no reality of the status of the Ummah then Wallahi this is a symptom of a hard heart.
Whereas the soft heart, it is connected to the Ummah as our Prophet Muhammad (peace be upon him)
said: This Ummah is like a body, when one limb is hurting, if your finger got slashed, if your little pinky got slashed, Wallahi you couldn't sleep at night. You would be in pain and suffering and that's exactly what our Prophet (SAW) said.
When one organ is in distress, the whole body is in pain and making Dua to cure this organ so if you find yourself not even caring, not even keeping up with the news, it's not even a concern to you what the Ummah is going through then Wallahi my dear brothers and sisters let me put it straight to you your heart has become hard.
May Allah soften our hearts and make us among those who turn to Him in repentance and allow us to return to Him with a pure heart. (Ameen)