Allah says: “And of everything We have created pairs; perhaps you will take heed.” [51 Az-Zariyat:49]
That means, everything in the world has been created on the principle of the pairs. The whole system of the universe is functioning on the principle that certain things are complimentary, and matching, to certain other things, and their combination brings into being countless new forms and combinations. Nothing here is so unique that it has no match. The fact is that a thing becomes productive only after it has combined with its matching partner.
The erection of the universe on the principle of pairs, and the existence of all things in the world, in couples, is a reality that testifies to the necessity of the Hereafter. If you consider deeply, you will come to the conclusion, that when everything in the world has a partner, and nothing becomes productive without combining with its partner, how can the life of the world be without a match and partner? Its match and partner is the Hereafter. Without that partner it would be absolutely fruitless.