אור החיים — כי תצא למלחמה על איביך

Q — Why does the war passage say 'כי תצא למלחמה' with the definite article ('the war'), as if referring to one particular, well-known war?

A — Or HaChaim reads it as alluding to 'the war than which there is none greater' — a person's battle against his yetzer hara. He maps the verse's imagery onto this struggle: the 'horse' (סוס) is the yetzer, trained and ready for war, unlike the inexperienced person; the 'chariot' (רכב) is the human composition (הרכבה) that inclines and craves forbidden things; and 'a people greater than you' (עם רב ממך) is the additional forces of evil a person generates through his own past sins. The Torah comes 'to remove fear from his heart' — reassuring that even against this formidable, experienced enemy, victory is possible with God's help.