Price stability as in keeping inflation down. This might have also included maintaining reasonable foreign exchange levels. Selling non-productive assets such as gold freed up a lot of cash that as foreign exchange reserves could be and were used to protect European currencies against speculation. Bar the British pound, it was successful in Europe.* All this gold was a very old inheritance of the gold standard era and was entirely superfluous.
*The BOE is the only one in Europe that tries to mimic the Fed's for-profit actions but very often to the detriment of the pound. The moral here is whenever a central bank tries to gain on trading it loses out big time and threatens its respective economy to collapse. That's why Bernanke should be decapitated in the best European tradition.