Anointed by God 

Because the people of Israel had turned away from God, He allowed the Midianites to terrorize Israel for seven years, and destroy the fruits of their land and livestock.

Israel cried out to God in his need and Jehovah intervened by his grace and decided that Gideon would be the man appointed by the one who would lead the poor, oppressed and fearful Israelites to victory.

Jehovah is with you, strong and valiant man You will save Israel from the hand of the Midianites.

These words, spoken to Gideon by an angel sent by God.

But Gideon's first thought was: Why me? Are there no other stronger ones that can do it?

God knew the fears and limitations of Gideon, but he chose it anyway.

God knows our personality and our weaknesses, our tendency to sin. Those who see themselves as the greatest, the strongest, the wisest, will hardly hear the voice of God. Those who are humble, with an open and receptive heart, on the contrary will have the capacity to become men of God, ready to do his will.

Judges 7: 1-7 tells us that Gideon and his 32,000 men were about to start the war against the Midianites, who had more than 100,000 soldiers. 

God told Gideon and his men, "Now therefore, proclaim this in the ears of the people: Whoever fears and trembles, let him rise early and return home from Mount Gilead." Judges 7: 3 

Observe that 22,000 men left the troop and only 10,000 remained. And God told Gideon, "There are still too many; Take them to drink water and I'll put them to the test there. Of which I say to you: "Go this with you", will go with you; but from anyone I say to you: "May this one not go with you," he will not go.  
Gideon has recently armed himself with the Spirit of the Lord, and is at the head of an Israelite army of 32,000 warriors. It is really a powerful army then came a new commandment from God: Everyone who fears return home. God knew that Israel would take credit for the victory, and celebrate their own strength instead of giving the glory that corresponds to God as head of the army. 

Then the Lord said to Gideon, "With these three hundred men who licked up the water, I will save you, and will deliver the Midianites into your hands; and leave all the other people each to his place. Judges 7: 7 

God gave instructions to spy on the camp, and here Gideon heard that the Midianite soldiers were also afraid. One spoke of a dream where he saw that a barley bread rolled to the camp of Midian and hit it and the store fell.

This is nothing but the sword of Gideon son of Joash, a man of Israel cried the Midianite soldier. God has given the Midianites into their hands with all the camp.

Gideon's faith was renewed when he heard this and with his 300 men, armed only with trumpets and torches burning inside pitchers, the Israelites crawled to the edge of the Midianite camp. When the signal was given, the Israelites broke the pitchers, revealing the torches, and blowing their trumpets, shouting:

By the sword of Jehovah and Gideon

Source

The Midianites were surprised, and thought they had been ambushed by a large army. They panicked, putting each other's sword against their partner until finally fleeing into the night. His great power had been defeated by only 300 men, led by Gideon, a man of God.