"All these people told us not to lend money at interest; and lending money at interest--what we call investment--is the basis of our whole system."

As Lewis indicates, many passages in the Old and New Testaments prohibit "usury," or lending money at interest. Passages that use the term may be found here. Lewis's reference to Moses comes from the fact that he is considered the author of the first five books of the Old Testament, also called the Pentateuch or Torah.