This question was asked in CSS-2011 and my answer to this part of the question was exactly as follows.

Islamic philosophy of reward and punishments:
• Islamic law of reward and punishment is balanced and justified;it gives punishment according to severity and degree of sin.For example Tauheed is considered the foremost pillar of Islam.Without it a man cannot become a Muslim.If anyone violates this pillar,there is no way out of punishment.Thus the severity is according to the sin.Moreover the pillar or institution of zakat comes next after Tauheed.One who does not pay zakat will be burnt,on the day of judgement, with the money and material which he gathered.The punishment is so severe because zakat takes prominent place in streghthening the faith.Islam also rewards good deeds. The most beneficial reward is the will of Allah(JS).Reward of paradise is also considered beneficial.
• Punishment are necessary to maintain order in a society.

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We can trust the man of troubles but not on the man of pleasures.