Incidentally, I will note that it is traditional at even "secular" performances of Handel's Messiah for the audience to stand when the Hallelujah Chorus is sung. This is because during the first performance of this in front of the Emperor, he was so moved that he stood up when it began (liturgically this would be sung in a Church service immediately before the Gospel Reading, when the congregation should stand; so evidently the Emperor was so caught up that he forgot that it was not at a Church service) And protocol being what it was, when the Emperor stood up everyone else attending stood up as well.
Today, of course, we do not stand because of an earthly Emperor, we stand to honor the King of Kings.
