To say that Richard Cory "glittered when he walked" and "fluttered pulses" when he spoke even the simplest and most mundane words shows how he is idealized by those around him.  He is described as imperial and compared to "a king" who possesses "every grace." Everyone around him thinks that his life is enviable in every conceivable way.  Even in the line "he was a gentleman from sole to crown," the word "crown" is used to describe the top of his head (as if to say he is every inch the gentleman), but the association of a crown with royalty cannot be overlooked.  He seems to everyone else the epitome of grace and good fortune.  In reality, however, the way Richard Cory viewed his life was obviously very different, because he chose to end it in such a catastrophic and violent way.  

The line "he glittered when he walked" shows the great disparity that can exist between the way others perceive us and the way we feel about ourselves.  We never know when we look at someone what they might be feeling underneath whatever facade they display.  Someone might think that we have it all together, that we lead a charmed life, but they can never know how we truly feel, how we truly are.