I asked the same question on reddit once. it . . . intrigued people.
Probably similar to the music that plays on the Mission Swords of Sangheilios
I’d say music similar to the music from the Renaissance period.Or to be specific probably Gregorian Chant.
@Jblast10 Some people believe the Gregorian chant in the Halo theme could be actually elites sing some religious song
https://www.youtube.com/watch?v=bSIV7CjH4cU
What do you think?