Mohamed El Erian writes:  A bit more than two years ago, the European Central Bank performed an amazing magic trick: With the promise that he would do “whatever it takes” to hold the euro area together, ECB President Mario Draghi managed to bring Europe back from the brink of financial and economic disaster.

Now, Draghi is at it again. His pledge to do what’s needed to battle faltering growth and deflationary pressures has already moved markets, weakening the euro enough to have a positive effect on exports and fend off deflation. This time around, though, words won’t be enough: The ECB will have to follow through on Draghi’s promise.

Back in July 2012, the ECB didn’t have to follow Draghi’s words with action: The mere knowledge that the central bank was ready to commit its vast resources to defending struggling governments from market pressures was enough to restore calm. Over the ensuing two years, the governments’ borrowing costs fell to record lows, capital started flowing back into embattled countries such as Italy and Spain, and even Greece managed to sell new bonds to investors at surprisingly low yields.

Draghi’s latest promise is focused more on reinvigorating a European economy that has been running far too close to recession and deflation. A few weeks ago, he indicated that the central bank was prepared to take extraordinary stimulus measures, similar to the bond-buying programs on which the U.S. Federal Reserve and the Bank of England embarked much earlier. The ECB made a small initial step by cutting interest rates and announcing a limited plan to buy asset-backed securities and covered bonds.

If the ECB wants the effect of its first steps to last, it will have to do a lot more, and very soon. Still, there’s no guarantee the measures will work as intended.

Europe will not capture the benefits of a weaker currency unless the ECB announces this month a large program to expand its balance sheet by purchasing a broad set of bonds in the marketplace. Absent such an announcement, the euro will likely appreciate. And while aggressive action will improve the growth and inflation outlook at the margin, it’s not likely to be enough to materially change Europe’s economic prospects. For that, Europe needs more than monetary stimulus. It needs governments to do a better job of supporting ECB actions by pursuing pro-growth structural reforms aimed at improving labor and product markets, better coordinating fiscal policy and eradicating remaining pockets of excessive indebtedness.

Unfortunately, there’s little indication that this will happen anytime soon.