The wisdom behind the prohibition of interest (riba)
Riba is any contractual increment in a lending relation. It is prohibited and considered one of the major sins and acts of disobedience to Allah. The parties to a Riba-based contract are declared war on by Almighty Allah and His Messenger, as stated in the Qur'an, Surat Al-Baqarah 2, verse 278-279: “O ye who believe! Observe your duty to Allah, and give up what remaineth (due to you) from usury, if ye are (in truth) believers. And if ye do not, then be warned of war (against you) from Allah and His messenger.And if ye repent, then ye have your principal (without interest). Wrong not, and ye shall not be wronged.”
The strict prohibition of interest in Islam is a result of its deep concern for the moral, social, and economic welfare of mankind. Muslim scholars have sound arguments explaining the wisdom of this prohibition, and recent studies have confirmed their opinions, with some additions and extensions of their arguments.
Imam al-Razi says in his tafsir of the Qur'an:
First: The taking of interest implies appropriating another person's property without giving him anything in exchange, because one who lends one dirham for two dirhams gets the extra dirham for nothing. Now, a man's property is for (the purpose of) fulfilling his needs and it has great sanctity, according to the hadith, “A man's property is as sacred as his blood.” (Reported by Abu Na'eem) This means that taking it from him without giving him something in exchange is haram.
Second: Dependence on interest prevents people from working to earn money, since the person with dirhams can earn an extra dirham through interest, either in advance or at a later date, without working for it. The value of work will consequently be reduced in his estimation, and he will not bother to take the trouble of running a business or risking his money in trade or industry. This will lead to depriving people of benefits, and the business of the world cannot go on without industries, trade and commerce, building and construction, all of which need capital at risk. This, from an economic point of view, is unquestionably a weighty argument.
Third: Permitting the taking of interest discourages people from doing good to one another, as is required by Islam. If interest is prohibited in a society, people will lend to each other with good will, expecting back no more than what they have loaned, while if interest is made permissible the needy person will be required to pay back more on loans (than he has borrowed), weakening his feelings of good will and friendliness toward the lender. (This is the moral aspect of the prohibition of interest.)
Fourth: The lender is very likely to be wealthy and the borrower poor. If interest is allowed, the rich will exploit the poor, and this is against the spirit of mercy and charity. (This is the social aspect of the prohibition of interest.) (Tafsir by al-Fakhr al-Deen al-Razi, vol. 7, p. 4.)
Thus, in a society in which interest is lawful, the strong benefit from the suffering of the weak. As a result, the rich become richer and the poor poorer, creating socio-economic classes in the society separated by wide gulfs. Naturally, this generates envy and hatred among the poor toward the rich, and contempt and callousness among the rich toward the poor. Conflicts arise, the socio-economic fabric is rent, revolutions are born, and social order is threatened. Recent history amply illustrates the dangers to the peace and stability of nations inherent in interest-based economies."