Sotah 42 - Kohen at war
A Kohen is appointed and anointed to go to war with the army. When the army approaches the enemy, he talks to the soldiers and says the following words, talking in Hebrew. How do we know that he is talking in Hebrew? Because of the term, "and he will say (vediber)." The same term is used describing Moses, "and Moses said, and God replied with a voice." Since Moses spoke to God in Hebrew, the Kohen at war also speaks in Hebrew.
He says, "Listen, Israel (Shema, Israel!), you are approaching an enemy." He uses the word "enemy" to emphasize that if Jews were fighting against Jews, as it happened between the tribes at times, they could expect that the victors will be merciful with the captives. He then quotes historical episodes proving the point. However, with enemies it is not like that, they will not pity you. This understanding caused them to fight with all their might.
"They come against you with human might, as Goliath. You, however, are going to win, like David did, because your God is walking with you."
Rabbi Shimon bar Yochai said, "Why is God walking with them? - because they say the 'Shema' prayer, just like the Kohen at war mentioned. From here we see that if only all Israel said 'Shema' in the evening and in the morning, they would never fall into the hands of the enemies."
Art: David beheading Goliath by Michiel van Coxie