Glass-Steagall prohibited commercial banks from engaging in underwriting securities, i.e., banks that accepted deposits and loaned money at interest were not allowed to issue bonds or new public offerings of stocks. The Act also authorized the creation of deposit insurance.
The Banking Act of '33 was strengthened in 1956 when bank holding companies were barred from the insurance business.
Between 1982 and 1999, banks were deregulated until the same corporation could take deposits, create credit, borrow from the Federal Reserve, underwrite stocks and bonds, operate a hedge fund, and sell insurance.
In 1990, the largest bank in the USA--CitiBank--held assets of $369.1 (2009 dollars); by 2009, it held over 5x that. Bank of America is now 13.24 times its size in 1990. The repeal of Glass-Steagall undeniably worsened our problem with banks that were too big to fail.