Why does Bierce use a flashback in section 2 of an occurrence at owl creek bridge instead of proceeding with the event taking place?

I think Bierce had used this flashback to get us in the mood of the story. Meaning that we got into Farquhar's mind, with the use of the third person limited point of view, understanding what made him hanged and what urged him to attempt damaging that bridge from the beginning. Farquhar at this time had nothing to do but think and imagine with two flashforwards and one flashback.