God's Names and Attributes are all absolute and eternal. As He is absolutely and eternally Merciful. Relenting and Forgiving so He is again absolutely and eternally Mighty. Just and Dignified.
Although His Mercy embraces all things (7:156) and as is stated in a Saying exceeds His wrath some people commit such great crimes and sins (like unbelief and associating partners with God) that their due can only be eternal punishment. Besides despite the Divine declaration that whoever kills a human being unjustly it is as if he killed all mankind (5:32) especially in a world like today's where might is right is the rule thousands of innocent people are killed almost every day and many others are wronged and deprived of their basic human rights and worse a great many of the most abominable sins and injustices go unpunished. When death comes it does not discriminate between the oppressed and oppressors the innocent and criminals and between the sinless and sinful. This means that as is the case in this world where little crimes are judged in small courts while great ones are referred to supreme tribunals such great crimes and sins as unbelief and associating partners with God and murder and oppression are postponed to a day when God will judge them with His absolute Justice.
A day will certainly come when those who gave God the thanks due to Him will be welcomed with. "Eat and drink to your hearts content because of what you did in days gone by (69:24)" and "Peace be upon you! You have done well. Enter here to dwell forever (39:73)" to a place where God has prepared for them things no eyes ever saw no ears ever heard and no mind ever conceived while the others who tainted the world with the blood they shed and the sins and crimes they committed will be thrown into Hell with the shout "Enter (through) the gates of Hell to dwell therein forever: what an evil abode for the arrogant! (39:72)."