Mendelssohn's Oratorio Elijah is full of great choral pieces. This has always been a favorite.
The text is taken from Psalm 121:4 "He, watching over Israel, slumbers not nor sleeps," and Psalm 138:7 "Shouldst thou, walking in grief, languish, He will quicken thee."
These two phrases are interwoven to great effect in Mendelssohn's soaring style.
This edition indicates a tempo of about 80 bpm, though some prefer to perform it a bit faster.
HE WATCHING OVER ISRAEL, by Felix Mendelssohn-Bartholdy, for SATB choir with piano, comes in a pdf file of 958K, with a thirteen-page score, and a license page, fourteen pages in all. Performance time should be about four minutes.