Why is "Nesatim" in past tense?
Malbim: I caused them to come [to fight you], to deliver them into your hand.
What is the difference between "Lo Yisyatzev Iah Befanecha" and "Lo Ya'amod"?
Malbim: Yisyatzev refers to beginning to fight. "Lo Ya'amod" means that they will fall, even though they did fight.