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The Messenger of Allah (saws) said: "The world is a prison for the believers and Paradise for the disbelievers"
[Sahih Muslim]
Explanation : Prison is not a place where people want to live or end up at. The mere existence of prison has a significant deterrent value. Also once a person is a prisoner , it is a human tendency to try to become free. Prisoners want to be free and to return to their homes and to the society where they originally belonged . This sense of believing is important for a believer.
To be a believer in Islam means understanding that one's destination is Paradise, that is where everyone belongs. Paradise is designed and prepared for successful human beings; it is awaiting them. When a person develops that awareness and conviction , then this ephemeral worldly life to him appears as nothing short of a prison from which he seeks freedom and wants to reach his destination.
If he has to spend some time in this prison , he hardly enjoys it ; the urge of reaching his ultimate destination overshadows his other desires. The opposite is true about people who do not believe. They treat this world as their Pradise. To them , nothing awaits them beyond this life. Therefore, they indulge themselves to the extent that they become entrapped.