As Boschot has said, what it expresses above all is terror in the presence of annihilation.
When the _Requiem_ was played at the Trocadero, the audience was greatly impressed and filed out slowly.

They did not say, "What a masterpiece!" but "What an orchestra leader!" Nowadays people go to see a conductor direct the orchestra just as they go to hear a tenor, and they arrogate to themselves the right to judge the conductors as they do the tenors.
But what a fine sport it is! The qualities of an orchestra conductor which the public appreciates are his elegance, his gestures, his precision, and the expressiveness of his mimicry, all of which are more often directed at the audience than at the orchestra.

But all these things are of secondary consideration.

What makes up an orchestra conductor's worth are the excellence of execution he obtains from the musicians and the perfect interpretation of the author's meaning--which the audience does not understand.

If such an important detail as the author's meaning is obscured and slighted, if a work is disfigured by absurd movements and by an expression which is entirely different from what the author wanted, the public may be dazzled and an execrable conductor, provided his poses are good, may fascinate his audience and be praised to the skies.
Formerly the conductor never saluted his audience.