It is a common saying from the era of the Revolutionary and Civil Wars. It was popularized as a key moment in the movie The Patriot. The continental Army had a dim view of militias because under pressure they would break and run from the fight, because they did not have the discipline to HOLD THE LINE.

In any battle of armies it was and is of critical importance that the forward line of the battle HOLD it's formation during the advance. During the ADVANCE.

To Hold the Line you do not Sit on your Ass.

To Hold the Line you do not Retreat.

To Hold the Line you do not Scatter.

To Hold the Line you do not Doom.

To Hold the Line you do not Cower.

To Hold The Line you ADVANCE TOGETHER AS ONE.

PICK UP THAT FLAG AND HOLD THE FUCKING LINE