We are to rely on His 'mighty power' (vs. 10) to fight the fight through us. He's much better about knowing how the battle should go, where justice or mercy should be applied, and what to prioritize. Our job is to 'stand firm' through His power, not to let the enemy knock us down, not to get pushed back, not to retreat.
When the battle is at it's fiercest we don't always have to be plunging forward, sword swinging. Sometimes there are periods of just standing, and that in itself is a victory!
(These are mostly thoughts from my husband's brain. Just putting it in my own words here!)