This is background information added to tell the reader what happened to the song in the future. (See: [[rc://en/ta/man/translate/writing-background]])
The word "Jashar" means "upright." AT: "The Book of the Upright" (See: [[rc://en/ta/man/translate/translate-names]])
# Your glory, Israel, is dead
"Your glory" refers to Saul. (See: [[rc://en/ta/man/translate/figs-metonymy]])
# the mighty
The phrase "the mighty" refers to both Saul and Jonathan. This nominal adjective is plural, and can be stated as "the mighty ones."(See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-nominaladj]])