Someone has to speak the words that set a group's state, or fear will set it for them.
Fear shows up with its own script already running, and unless a louder voice overwrites it out loud, that script sets the breathing and the posture, the posture sets what feels possible against those numbers, and what feels possible decides whether ground gets taken or given. Courage is installed by language long before it is displayed in conduct.
Which is why the assignment goes to a priest rather than a general. The words carry because they are anchored to God going out with them, which makes them a report on reality rather than encouragement. Leave that hour silent and fear writes the state unopposed, and the outcome is settled before contact.