Why did Islam forbid alcohol in this world, yet promise it to the people of Paradise?

The prohibition of wine in this world is due to the harms it contains, whereas the wine of Paradise is not forbidden because it is pure and does not contain the harms of worldly wine. It is a pure delight, free from all impurity and defilement. It resembles worldly wine only in name, but its true nature is that which "no eye has seen, no ear has heard, and no human heart has conceived."