Deuteronomy 7:17

17If thou shalt say in thine heart. Since it was a matter of great difficulty to destroy such a multitude of men, and despair itself would drive them to madness, so that it would be frivolous for the Israelites to cut off all hope of mercy, God anticipates their fear, and exhorts them to the strenuous execution of His sentence. From whence we gather some useful instruction; whenever God commands anything which exceeds our power, we must still obey and boldly break through whatever obstacles present themselves to impede us. In all arduous matters, therefore, let this doctrine come to our aid, that whatever is contrary to God’s will may easily be annihilated by His almighty power. But since terror, presented to our eyes, immediately so lays hold of all our senses that we lie as it were torpid, God recalls to the recollection of the Israelites what abundant grounds of confidence He had supplied them with. For all the miracles He had wrought were so many proofs of His invincible power; and hence they should conclude that nothing was to be dreaded, provided God should go before them, and that, therefore, being assured of victory, they should not descend to any treaties.