Parallel to the framework of religious significance in the story, which makes the realism imaginatively powerful, there is a framework of economic doctrine.
The economic framework is made upof two parts. There is a good deal of straight documentation of Crusoe´s financial and mercantile dealing. He starts out with forty pounds which he raises (unknown to his father) from relatives in London. He returns from his Guinea voyage with 5 lb.9 oz. of gold, which sells for almost three hundred pounds. When he escapes from the Moors, his rescuer (the Portuguese captain) sets him with  a little capital (two hundred and twenty pieces of eight), the proceeds of selling the Moors boat, the skins of a lion and a leopard, the lump of beeswax and his fellow-slave Xury: and so on, until, at the end, presumably with God´s help, he is master of `above five thousand´ and sell his Brazil plantations for firty-two eight hundred piecesof eight (allowing for the deduction of a pension to the Portuguese captain of one hundred moidires per annum for life: and fifty moidores to his son afterwards).
This rather precise documentation, adding to the `realism´* of the book, seems also to have fascinated Defoe. It is more than an index of Crusoe´s success. Defoe had a real imaginative feeling for financial and mercantile success: perhaps this came from his own misfortunes.
The religious overtones are seen in the immediate cause of Crusoe´s shipwreck, which was his greed, prompting him to `rise´
faster than `the nature of the things admitted´ by going on a slaving expedition to Africa.

Secondly, however, there is a more speculative economic content, put forward as part of the imaginative exploitation of the theme of `enviroment´. Crusoe, for example, in a long passage about making planks, says this:

`Time or labor was little worth, and so it was as well employed one way as another.´

On the fourth aniversary of his landing, he reflected on the plenty in his island, but added:

`All I could make use of was all that was valuable. I had enough to eat, and to supply my wants... The nature and experience of things dictated to me, upon just reflection, that all the good things of this world are no farther good to us than they are for our use.´

A drawerful of diamonds was of no value to him, because it was of no use. This point about the uselessness of precious metal and money had been amusingly made when Crusoe was taking things from the wreck, he says:

`I smiled to myself  at the sight of this money. "O drug", said I aloud," what art thou good for, thou art not worth all the heap. I have no manner of use for thee, e´en remain where thou art, and go to the bottom as a creature whose life iseconomist´  .

SOURCE:  ©Robinson Crusoe, Daniel Defoe.
                 ©Penguin classics.
                 ©Edited with an introduction by Angus Ross.