Why is this world like a prison for the believer?

Because the believer freely keeps many commandments and limits, while the disbeliever does as he pleases. Yet for someone who loves God, these limits stop feeling like a burden over time, and the apparent prison becomes their paradise.

The comparison in the hadith above sounds harsh at first. What it refers to is freedom of action. The believer lives with many commandments. He is to speak the truth, not to take what does not belong to him, to honour his parents, to be kind to children and to keep in mind what he is preparing for the future and for the life to come. Around each commandment there are further limits. Seen from outside, this is a life with many walls.

The disbeliever, by contrast, feels bound by no such limits. He does what he likes and enjoys whatever he can get. In this sense the world is like a paradise for him. What matters is that the believer stays in his prison of his own free will. He could tear down the walls at any time, but he does not.

The comparison holds only in this one respect. For someone who truly loves God wants to do what God wishes. What looks like a restriction to an outside observer is no longer one for him. Over time he has acquired a taste for this way of life.

An everyday example makes this clear. Civilisation means many rules, down to how one holds a knife and fork. Children at first find such rules a nuisance. But once they are grown, good manners come naturally to them, and they would not want to live without them.

It is the same with the believer. The world of commandments becomes a world of joy for him, and he finds his paradise already in this life. The verses above promise the Garden as a home to the one who restrains his soul from base desires.