Imam Al-Ghazali (550 A.H) says regarding the nature of Money in his Ihya Uloom ud din:
The creation of dirhams and dinars (money) is one of the blessings of Allah. They are stones having no intrinsic usufruct or utility, but all human beings need them because every body needs a large number of commodities for his eating, wearing etc, and often he does not have what he needs and does have what he needs not. Therefore, the transactions of exchange are inevitable. But there must be a measure on the basis of which price can be determined, because the exchanged commodities are neither of the same type, nor of the same measure which can determine how much quantity of one commodity is a just price for another. Therefore, all these commodities need a mediator to judge their exact value Allah Almighty has, therefore, created dirhams and dinars (money) as judges and mediators between all commodities so that all objects of wealth are measured through them. , and their being the measure of value of all commodities is based on the fact that they are not an objective in themselves.
Had they been an objective in themselves, one could have a specific purpose for keeping them, which might have given them more importance according to his intention, while the one who had no such purpose would have not given them such importance, and thus the whole system would have been disturbed. That is why Allah has created them, so that they may be circulated between hands and act as a fair judge between different commodities and work as a medium to acquire other things. So, the one who owns them is as if he owns everything, unlike the one who owns a cloth, because he owns only a cloth, therefore, if he needs food, the owner of the food may not be interested in exchanging his food for cloth, because he may need an animal for example.
Therefore, there was needed a thing which in its appearance is nothing, but in its essence is everything. The thing which has no particular form may have different forms in relation to other things like a mirror which has no color, but it reflects every color. The same is the case of money. It is not an objective in itself, but it is an instrument to lead to all objectives.
So, the one who is using money in a manner contrary to its basic purpose is, in fact, disregarding the blessings of Allah. Consequently, whoever hoards money is doing injustice to it and is defeating its actual purpose. He is like the one who detains a ruler in a prison.
And whoever effects the transactions of interest on money is, in fact, discarding the blessing of Allah, and is committing injustice, because money is created for some other things, not for itself. So, the one who has started trading in money itself has made it an objective, contrary to the original wisdom behind its creation, because it is injustice to use money for a purpose other than what it was created for. If it is allowed for him to trade in money itself, money will become his ultimate goal, and will remain detained with him like hoarded money. And imprisoning a ruler or restricting a postman from conveying messages is nothing but injustice.
