In 2 Chronicles 20, we see a picture of how we can wage warfare against Satan. There we read of a great multitude that came against King Jehoshaphat. But Jehoshaphat did the right thing, when confronted by so many enemies.
He got the whole nation of Judah to seek God in fasting and prayer. Then he prayed to God acknowledging their weakness, their foolishness and their faith. He said, "O our God, wilt Thou not judge them? For we are powerless before this great multitude who are coming against us; nor do we know what to do, but our eyes are on Thee" (v.12). This is the secret of all effective prayer - to recognise our weakness and our foolishness, and to trust God utterly to fight the battle for us.
Jehoshaphat confessed that he did not know what to do - and that is a good confession to make, for God has promised to give wisdom to all those who acknowledge their lack of it. But we have to ask for wisdom in faith (Jas.1:5,6). And that was what Jehoshaphat did. He did not merely acknowledge his impotence and his lack of wisdom, He concluded his prayer with an expression of absolute trust in God. He said, "But our eyes are on Thee". In other words, he was telling God, "We are expecting you to work on our behalf". AND GOD DID!!
As soon as Jehoshaphat finished praying, God immediately sent him a reply saying, "Do not fear, for THE BATTLE IS NOT YOURS BUT GOD'S. You need not fight in this battle. Stand and see the salvation of the Lord on your behalf" (v.15,17).
Jehoshaphat worshipped the Lord as soon as he heard those words of the Lord. The next morning he placed "singers and those who praised the Lord in holy attire" in the forefront of the army to lead Judah's soldiers to battle. And as soon as they began to sing and praise the Lord, the Lord defeated their enemies (v.21,22).
To confess that we are rotten, good for nothing, useless and foolish, is not humility, but unbelief!! If we keep on confessing that, we will remain useless forever. False humility like that is often mistaken for the genuine thing by undiscerning believers! But Jesus told us to learn humility from Him (Matt.11:29). And where do we find Jesus ever confessing that He was useless and good for nothing? Never.
True humility is taking the place of entire nothingness before God, so that God might be all in all. This is the place that Jesus took as a man. This is what we must do too. In that lowly place, we can trust God to do a mighty work in us and through us, and to crush Satan under our feet.