The battle is not yours it's the Lord's. But, He has to fight your battle through you. He has given you a weapon and it's up to you to use it. The weapon He has given you to use is his word (Ephesians 6:17). And it's powerful and sharper than any twoedged sword (Hebrews 4:12). In life you have a choice either you can fight the battles in life in your own strength or in the power of God.
Notice in Deuteronomy 7:1,2 it says, "When the Lord thy God shall bring thee into the land whither thou goest to possess it, and hath cast out many nations before thee, the Hittites, the Girgashites, and the Amorites, and the Canaanites, and the Perizzites, and the Hivites, and the Jebusites, seven nations greater than thou: And when the Lord thy God shall deliver them before thee; thou shalt smite them, and utterly destroy them...." Notice it says that the Lord was going to cast out the nations before them and deliver them before them, how was he going to do it. By Joshua following his instructions "This book of the law shall not depart out of thy mouth" and as a result of him doing that it says that Joshua would make his way prosperous (Joshua 1:8). Joshua and the children of Isreal defeated seven nations greater and mightier than them with the sword of God's word.
In 1Samuel 17 a boy named David went up agianst a great man of war named Goliath while the armies of Isreal hid. But, David knew how to get the victory and it was going to have to be by his mouth. Saul even tried to put his sword on him and David turned it down. This battle was more than a battle with weapons, it was a battle of words. Notice that Goliath shouted some things at David and David responded with his own words. David won the battle with his words before he picked up a stone. Notice in verse 47 David said, "And all the assembly shall know that the Lord saveth not with sword and spear: for the battle is the Lord's, and he will give you into our hands." The battle was the Lord's and He fought it with the words David spoke out of his mouth. In verse 50 it says David slew Goliath with no sword in his hand, that's because the sword was in his mouth and the sword in your mouth will always defeat a sword in the hand. So in every battle of life be sure you use your sword.