רבינו בחיי — כי תצא למלחמה... ונתנו ה' אלהיך בידך

Q — The pasuk says ונתנו ה' אלקיך בידך — him, singular. But you are going to war against a nation, multiple enemies. Why singular?

A — Rabbeinu Bachya gives two layered answers. First reading: all enemies, however numerous, are functionally a single entity from the perspective of the Defender — they collectively act as one will against you, and Hashem hands them over as one. Second reading, and this is the deeper RBB: the singular refers to the upper koach of the enemy nation — the shar above that supplies it with metaphysical strength. The pasuk is announcing that the war happens on two registers simultaneously. ונתנו — he, the angelic sar, singular — is delivered into your hand on the upper plane. ושבית שביו — his (sing.) captives — the human soldiers below are then captured on the lower plane. Every milchama is therefore really a double engagement: the visible armies fight on earth, while their sponsoring shar is being neutralized in shamayim. The grammar's singular אויב is not careless; it is the upper member of the pair, whose defeat above is the precondition for the captivity below.