Allāh created life and death to test us how we fare in terms of our actions.
You will never be able to find a crack in the sky.
Each time a group will be thrown into the Fire of Jahannam, the angels will ask them whether or not they were warned of this punishment. They will admit that they were warned, but they belied the Messengers.
Whether you whisper or talk loudly, Allāh knows what your hearts conceal.
How can we be assured to be safe of the earth swallowing us up as punishment from Allāh?
How can we be assured of safety from stones raining upon us as punishment from Allāh?
What if the being who gives us sustenance decides to withdraw from granting it to us?
The knowledge of the Hour is exclusively with Allāh.