Just because the melodies and words are lovely doesn't mean that they are easy to sing. Each of the voice parts has challenging lines with changes in dynamics and pitches that are difficult to negotiate. Singing this piece in a typical small church choir can be a challenge.
The opening line "He watching over Israel slumbers not not sleeps" has a dramatic jump in pitch for the sopranos (and tenors) in the middle of the line. What is so hard is that the "SLU" in "slumbers" happens on a sudden leap to a high F# sung pianissimo. The conductor pointed out that the singers shouldn't scoop or slide up to that high F#. ("Oh really? Then you try it!" the ladies were muttering under their breaths.)
The problem was that the "S" is an un-pitched consonant. So, it doesn't help to place the pitch immediately. Many singers forget that they have to prepare their thinking, breath management and consonant/vowel placement for the landing in a way that works best in a choral situation. Unfortunately, they allowed the "SL" to slide or scoop up to the pitch before they landed on the vowel. They were very out of tune as a section as well.
What was explained to the soprano section was that they needed to get through the "S" first consonant quickly and on to the second consonant. The un-pitched "S" cannot help, but the following "L" is a pitched consonant and can serve to lock in the pitch before opening into the "U" vowel on "slumbers." (It takes thought and preparation to manage it though!)
That explanation quickly cleared up the matter. (Yay! Too bad there are so many other issues we need to tackle in that piece! We need our regulars back!)
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So fun to see so many faces I love and remember in this Tabernacle Choir clip of "He Watching Over Israel." If you look quickly in the opening pass over the soprano section, you will even see me!