The Fed isn't printing 1.5 trillion greenbacks and handing out fat sacks on Wall St. They are providing short-term loans to increase the amount of money in circulation (liquidity). The intent is to increase the total amount of trading occurring so that the market can return to equilibrium sooner than later. The Fed wants to prevent firms from not making trades solely for lack of liquidity in the market.
edit: "from making profitable trades" -> "from not making trades"
edit: "from making profitable trades" -> "from not making trades"