Even though Allah is perfectly informed about them on every day, this Day has specifically been mentioned to highlight that those deeds will be fully recompensed since Allah is fully aware of them.
Surrounding the enemy's forces, Hazrat Ali as offered them to follow the religion of Islam at first, but they did not accept it.
Or, the camels, in Hajj pilgrimage, that run swiftly from one station to another, kick gravel from under their feet which strike each, other and sometimes causes sparks to appear.