What is it called when the music takes the shape of what's in the lyrics?

Maybe I'd better try to describe it.  Take the Messiah.  In "Glory to God
in the Highest," the word "high" is on the highest note.  When the bass
sings "The Nations Shake," he is very melismatic, shaking.  Outside of
classical music, Elvis Costello in "Alison" stops the music at the word
"Stop" (IIRC).  This is the first time in history that Costello and Handel
have been mentioned in the same sentence.  What's that device called?

Mitch Friedfeld