Here "the sword of Gideon" refers to Gideon's army attacking. AT: "The loaf of barley bread in your dream must be the army of Gideon" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This future event is spoken of as if it were a past event. This emphasizes that it will certainly happen. AT: "God will certainly help the Israelites defeat the Midianites" (See: [[rc://en/ta/man/translate/figs-pastforfuture]])