Well hold up now... lol. I am not suggesting that we should retreat! As far as a battle goes, there are people coming at you from every angle once you are in the midst of the fray and that includes behind, beside, infront and you are ducking and diving and slashing and weaving, and you need back armor as well as front armor, there is no running away involved in that melee. So having back armor does not make the roman soldier fearful or cowardly.
That being said, my point was 1) we should not preach from that text that we are not supposed to run and that is why it had no back armor. If you want to preach about standing and going forward in battle there are better texts to use than to make up a fact that is not even true and build a sermon on it. 2) How many things are we repeating from popular sermons that are not true, (fables, myths, legends, misquotes, etc)