There are two kinds of strength — daiva and purusakara. Daiva refers to the strength achieved from the Transcendence, and purusakara refers to the strength organized by one's own intelligence and power. Transcendental power is always superior to the power of the materialist. Depending on the mercy of the Supreme Lord, one must fight one's enemies even though one may not be equipped with modern weapons. Therefore Krsna instructed Arjuna, mam anusmara yudhya ca: [Bg. 8.7] "Think of Me and fight." We should fight our enemy to the best of our ability, but for victory we must depend on the mercy of the Supreme Personality of Godhead.

From Srila Prabhupada's purport to SB 9.10.20