What struck me most, other than the powerful expression of faith, was the sheer professionalism of the singing. These are trained voices, perfectly rehearsed. Impressive.
I know anyone who was in my high school’s choir would definitely have stood and joined in the singing. For years many high school and college choirs have sung this annually and often would invite any of the choir alumni to join in and sing with them at their concerts. It was a long running tradition at many schools, not just mine. While I graduated from high school over 35 years ago I still remember the part I sang perfectly and sing it several times each holiday season just by joining in with others singing it. I always see others do this too.