The people ask this question among themselves in order to make a statement. Alternate translation: "It is useless that we have kept his requirements and walked mournfully before Yahweh of hosts." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "walk mournfully" stands for "behave in a sorrowful manner," probably in order to indicate sorrow over their sins. (See: [[rc://en/ta/man/translate/figs-metaphor]])
# before Yahweh of hosts
Here this expression refers to God being aware of what the people were doing. (See: [[rc://en/ta/man/translate/figs-metaphor]])