Let's assume that new bank is incorporated and it issued 100 000 shares with nominal value odf $100. Let's also assume that all shares are sold for the same price, so bank now has 10 million dollars.
In equity section on balance sheet, there is now 10 million dollars of ordinary shares. Now let's assume further that 5 years has passed, the bank has spent all 10 million dollars for different purposes (R&D, expansion etc.) and now it doesn't have that money, but there are still 10 million dollar of ordinary share on its balance sheet.
If ordinary shares are vital part of bank's capital, how can they now respresent someting that can save the bank from bankruprtcy it problems occurs, when there is no money??? I'd understand if the bank wasn't allowed to spend that money, but it is used for various purposes.