The Torah in Parashat Shoftim (Debarim 20:1) commands that when Beneh Yisrael go out to war, and they see the large, imposing enemy army, they must nevertheless not feel frightened – “Lo Tira Me’hem” (“Do not fear them”). They must instead place their trust in Hashem, and remember that He assists them in battle against their foes. This command appears also in other contexts (“Lo Tira’um” – Debarim 3:22; “Lo Ta’arotz Mi’penehem” – 7:21).
The Sefer Ha’hinuch explains that the soldier is expected to fully trust Hashem, and to concern himself not with his physical wellbeing, but solely with bringing honor and glory to Hashem and to His people. The soldier should not think at all about his family or his property, and should instead focus his attention entirely on the battle that he wages. Moreover, the Sefer Ha’hinuch writes, the soldier should recognize that the lives of all Am Yisrael depend on him. If he feels frightened and runs away from the battlefield, then other soldiers will follow suit, and the war effort will thus be lost. He will then be held accountable for the defeat and the lost lives. The Sefer Ha’hinuch cites in this context the verse in the Book of Yirmiyahu (48:10), “Arur Mone’ah Harbo Mi’dam” – condemning one who “holds his sword back from blood,” meaning, who refrains from waging a war that must be fought against enemy nations. Additionally, the Sefer Ha’hinuch brings the teaching of the Sages that a soldier who fights with all his heart, and his intention is purely to bring glory to the Name of G-d, is guaranteed not to suffer any harm, and earns eternal rewards for himself and his offspring.
This command is binding upon only males, as only males are obligated to fight in wars. A soldier who is frightened during battle violates the prohibition.