Goldman Sachs became a depository bank in order to get access to the Fed Credit window and to get a base of insured deposits that would shore up its equity.

Goldman Sachs said that over the past several weeks it began discussions with the Fed regarding the possibility of becoming a bank holding company. "We understand that the market views oversight by the Federal Reserve and the ability to source insured bank deposits as providing a greater degree of safety and soundness," the company said in a statement.

http://www.npr.org/templates/story/story.php?storyId=94894707

So now, with access to the Fed loans in hand and ability to offer government insured deposits GS moves to increase its deposit base.

Unlike most of its competitors, Goldman Sachs (GS) does not have a deposit base or retail branches, making it vulnerable to liquidity risk. JPMorgan (JPM) for example has a vast pool of overnight and term deposits (both retail and institutional) they can access during tight liquidity periods. Goldman however tends to rely on capital markets for funding, forcing it not only pay higher financing rates, but making its funding costs extremely volatile, translating into unstable earnings and high stock volatility.

http://seekingalpha.com/article/313522-goldman-taps-the-wholesale-funding-market

So what is it doing? Selling insured Certificates of Deposit.