Zadok the Priest
I can think of no other piece of music whose reality belies its setting. A coronation anthem for a Hanoverian king becomes yet something other. The king is beautifully ambiguous, ostensibly King George, in reality, I suspect, in Handel's theological heart - Christ - the only King who can live forever in human hearts (if they accept him).
Handel is a great testimony to the virtue of immigration - a German who became our, the United Kingdom's, greatest composer. An ability to assimilate whose virtues we periodically lose sight of.