Bank's make money on loans. In order to make loans, a bank needs money to lend which it needs to borrow. A bank's customer deposits are often an inexpensive source of borrowing for the bank. It sounds like Volt was trying to grow in the mortgage loan business, but with a limited customer base, needed to borrow wholesale money. When interest rates rise, rates in the wholesale market tend to rise faster than the rate for customer deposits. As a result Volt was unable to compete for loan origination.