@Zephyris,
I'm asking because it is one of my favourite songs ever, although the last time I sang it I was about 15, and we made my music class cover teacher cry when we sang it (I think she thought we were pratting around when we said we sometimes spent our lessons singing, but at the time 14/16 of us were minster or established parish choristers, and the other two were well able to hold their own). I think if I could hear it again, it would make me cry too - one of the most beautiful polyphonic/contrapuntal short hymns ever written from my point of view!
At the moment, I can still hold all four parts in my head, but I would love to appreciate it as as an outsider again.