Loans are the most important part of a bank's income. Unlike deposits where the bank has to provide security and also provide compensation in the form of interest, a loan is a form of investment for the bank? Banks make the majority of their revenue by the difference between the deposit and loan interest rates. Loans may be important to a bank, however they carry the greatest risk. The main problem with loans is when they are given to customers that don't have the ability to repay them.