Credit relations split the act of buying from the act of paying. The development of credit, therefore, gives rise to a new function of money: money as a means of payment.
Credit allows me to purchase a commodity with credit rather than with money. But in doing so, I incur a debt that is payable in money. The capitalists actually purchase the commodity labor power with credit rather than money. When I sell my labor power to an industrial capitalist, I have to work for a week or more before I collect my wage in money form. It’s not unheard of for industrial capitalists to go bankrupt and fail to pay the debts they owe the workers for the labor power they bought with credit.
Not all debts payable in money are created by the purchase of commodities with credit. For example, tax liabilities payable to the state under conditions of capitalist production have to be paid for in money. In pre-capitalist times, taxes were sometimes payable in kind, but under capitalism they are almost always payable in money. Rent liabilities are also payable in money under capitalist conditions.
Under the feudal system of production that dominated Europe in the centuries before the rise of capitalism, feudal ground rents were either payable in labor, the inserfed peasants having to work on the lord’s lands for part of the workweek, or they were payable in kind. During the transition from feudalism to capitalism, rents payable in labor or kind were replaced by rents payable in money.