So why all the fuss over what Janet Yellen said?

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During a speech Thursday in Amherst, Massachusetts, Federal Reserve Chair Janet Yellen sent a message to the financial markets that the U.S. central bank remains on track to raise interest rates before the end of the year.

Just like she did in Cleveland on July 10. And in Providence, Rhode Island, on May 22. And in San Francisco on March 27.

In fact, the Fed leader's remarks that seemed to spark a fairly aggressive stock market rally Friday differed little from her previous speeches, or for that matter multiple statements released after this year's Federal Open Market Committee meetings over which Yellen presides.

What was it, then, that convinced the market that Yellen and the rest of the FOMC are finally serious this time about liftoff from zero rates before 2015 runs out?