three thousand men went up from the army

These men were part of the army. AT: "three thousand men belonging to the army went up"

three thousand men ... thirty-six men

These two phrases share similar meanings and are combined to emphasize that the people were extremely afraid. (See: rc://en/ta/man/translate/figs-parallelism)

Here the people are represented by their "hearts" to emphasize their emotions. AT: "The people were very afraid" (See: rc://en/ta/man/translate/figs-synecdoche)

The phrase "the people" refers to the Israelite soldiers.

"they were no longer courageous"