Somebody who knows this music piece?

[classicalmusicfan]

When I first heard this (this was used as a song in a tribute video made for the late Michael J in YouTube), it was like a divine piece with very lovely humming vocals. If you try to listen to it, it feels like heaven, very relaxing. I wonder what's the title of this song and who's the artist behind the lovely voice. And what type of music is this?Is this an example of a celtic music?

Please help me identify this one. Thanks in advance for any idea.