Possibly more about culture than language. Many tv shows use a short segment for choir based on the Pachelbel Canon, usually to underscore moments of epiphany by characters or participants in studio panels. What is the origin of this segment in that form? And is it just 'ah' or are there actually words?
I think you are talking about Sanctus by Libera, which is based on Canon by Pachelbel. https://www.youtube.com/watch?v=cmuPJvr89Jw
Many Korean TV programs have been using the introduction part of this song to make the scene holy in fun way. 'Ah' is not a word but after that part, there are some lyrics. https://music.naver.com/lyric/index.nhn?trackId=5204267 Hope this is what you are looking for.