Why were certain things forbidden in this world yet are permissible in Paradise?

The analysis and prohibition of things belong to Allah alone, and behind every legislation there is wisdom. The believer complies with the commands of Allah without objection, for Allah the Almighty "is not questioned about what He does, but they will be questioned." In Paradise, religious obligations cease and trials vanish. Some things that were forbidden to believers in this world will be permitted to them, such as the wine of Paradise, which differs from the wine of this world. It does not cause idle talk, sin, headache, or loss of reason. The Qur'an describes it as "white, a delight for those who drink" and "no ghoul [ill effect] is in it, nor will they be exhausted therefrom."