A close examination of what goes on in the universe will make it clear that within it are two opposed elements that have spread everywhere and become rooted: with their results like good and evil benefit and harm perfection and defect light and darkness guidance and misguidance belief and unbelief obedience and rebellion and fear and love the opposed elements clash with one another in the universe.
The universe manifests through such continuous conflict of opposites incessant alterations and transformations so as to produce the elements of a new world. These opposed elements will eventually lead to eternity in two different directions and materialize as Paradise and Hell. The eternal world will be made up of the essential elements of this transitory world and these elements will then be given permanence. Paradise and Hell are in fact the two opposite fruits which grow on the two branches of the tree of creation; or they are the two results of the chain of creation. They are the two cisterns which are being filled by the two streams of things and events and the two poles to which beings are flowing in waves. They are the places where Divine Grace and Divine Wrath manifest themselves and they will be filled up with their particular inhabitants when the Divine Power shakes up the universe with a violent motion.
In this world while oppressors depart still possessed of their oppressive power and the oppressed still subjected to their humiliation. Such wrongs are necessarily deferred for the attention of a supreme tribunal; essentially they are not ignored. Indeed punishment is sometimes enacted even in this world. The torments endured by the disobedient and rebellious peoples in past ages teach us that man is not left unanswerable but rather is ever subject to such correction as God Almighty’s Splendor and Majesty may choose to apply to him. So as declared in the verse. "Keep apart on this day. O you criminals (36:59)." God will separate the good from the wicked in the Hereafter and treat each group according to how they lived in this world. This is simply what His absolute Justice requires.