"Large sums were paid for the use of money, because the available amount of gold and silver was far less than was needed to carry on the commercial transactions of the times"

This quote by John Buchanan Robinson is describing the deficiency of silver and gold in the past, and exactly how this scarcity resulted in high rates of interest for borrowing cash. In the past, gold and silver were the key kinds of money, and the amount of silver and gold available was insufficient to meet the needs of the industrial transactions of the time. As a result, people needed to pay large sums of cash to obtain money, as the need for cash was greater than the supply. This shortage of silver and gold also brought about the advancement of various other forms of currency, such as paper money, which allowed for extra effective and also economical transactions. The quote is a suggestion of how the scarcity of gold and silver in the past brought about high rates of interest for obtaining money, and also exactly how this scarcity has been resolved with the advancement of various other kinds of money.