One man of you shall chase a thousand; for Yahweh your God, he it is who fights for you, as he spoke to you. — Joshua 23:10
What then shall we say about these things? If God is for us, who can be against us? — Romans 8:31

Author
Charles Spurgeon
Summary: We do not need to count how many are on our side: one person with God is a majority. Sometimes, as with Gideon, God reduces the number of helpers so that he may work through them; his army is never too small. He called Abram to found a nation and used Moses and Aaron to defeat Pharaoh. He also worked through Samson and David against numerous enemies. If we have faith, God is with us, even when the adversary has the advantage. When the Lord sends us, his strength accomplishes his purpose; therefore, we can rest in his promise and be courageous.
Why count heads? A man who is with God is a majority, even if there are a thousand on the opposing side. Sometimes we might have too many helpers for God to work through them, as happened with Gideon, who could do nothing until he had increased his strength by reducing his numbers. But the Lord’s army is never too small.
When God wanted to found a nation, He called Abram alone and blessed him. When He wanted to defeat the haughty Pharaoh, He used no army, but only Moses and Aaron. The “one-man ministry,” as certain wise men call it, has been used by the Lord far more than trained groups with their officers. Did all the Israelites together kill as many Philistines as Samson did alone? Saul and his armies struck down their thousands, and David his tens of thousands.
The Lord can give the enemy great advantages and still defeat him. If we have faith, we have God with us, and then what are multitudes of men? One sheepdog can shepherd a great flock of sheep. If the Lord sends you, O my brother, His strength will accomplish His divine purpose. Therefore, rest in the promise, and be courageous.
Source: The Cheque Book of the Bank of Faith. Translation by Allan Roman.
http://www.spurgeon.com.mx/chequera/meditames/mayo.pdf