Abu Huraira reported Allah's Messenger ﷺ as saying: Allah created one hundred (parts of mercy) and He distributed one amongst His creation and kept this one hundred excepting one with Himself (for the Day of Resurrection).
The Day of Resurrection is an important event in Islam, as it marks the end of this world and beginning of a new life in Jannah or Jahannam depending on our deeds in this world. Therefore, we should strive to do good deeds so that we can be rewarded on this day by Allah's mercy which He has saved especially for it.