Who is this uncircumcised Philistine that he should defy the armies of God?"

Why did they wait forty days to begin the battle

The Philistine army had gathered for war against Israel. The two armies faced each other, camped for battle on opposite sides of a steep valley. A Philistine giant measuring over nine feet tall and wearing full armor came out each day for forty days, mocking and challenging the Israelites to fight. His name was Goliath. Saul, the King of Israel, and the whole army were terrified of Goliath.
One day David, the youngest son of Jesse, was sent to the battle lines by his father to bring back news of his brothers. David was probably just a young teenager at the time. While there, David heard Goliath shouting his daily defiance and he saw the great fear stirred within the men of Israel. David responded, "Who is this uncircumcised Philistine that he should defy the armies of God?"
So David volunteered to fight Goliath. It took some persuasion, but King Saul finally agreed to let David fight against the giant. Dressed in his simple tunic, carrying his shepherd's staff, slingshot and a pouch full of stones, David approached Goliath. The giant cursed at him, hurling threats and insults.

David said to the Philistine, "You come against me with sword and spear and javelin, but I come against you in the name of the Lord Almighty, the God of the armies of Israel, whom you have defied ... today I will give the carcasses of the Philistine army to the birds of the air ... and the whole world will know that there is a God in Israel ... it is not by sword or spear that the Lord saves; for the battle is the Lord's, and he will give all of you into our hands."

As Goliath moved in for the kill, David reached into his bag and slung one of his stones at Goliath's head. Finding a hole in the armor, the stone sank into the giant's forehead and he fell face down on the ground. David then took Goliath's sword, killed him and then cut off his head. When the Philistines saw that their hero was dead, they turned and ran. So the Israelites pursued, chasing and killing them and plundering their camp.

Points of Interest from the David and Goliath Story: Why did they wait forty days to begin the battle? Probably for several reasons. Everyone was afraid of Goliath. He seemed invincible. Not even King Saul, the tallest man in Israel, had stepped out to fight. Also, the sides of the valley were very steep. Whoever made the first move would have a strong disadvantage and probably suffer great loss. Both sides were waiting for the other to attack first.David chose not to wear the King's armor because it felt cumbersome and unfamiliar. David was comfortable with his simple slingshot, a weapon he was skilled at using. God will use the unique skills he's already placed in your hands, so don't worry about "wearing the King's armor." Just be yourself and use the familiar gifts and talents God has given you. He will work miracles through you.

David's faith in God caused him to look at the giant from a different perspective. Goliath was merely a mortal man defying an all-powerful God. David looked at the battle from God's point of view. If we look at giant problems and impossible situations from God's perspective, we realize that God will fight for us and with us. When we put things in proper perspective, we see more clearly and we can fight more effectively.
When the giant criticized, insulted and threatened, David didn't stop or even waver. Everyone else cowered in fear, but David ran to the battle. He knew that action needed to be taken. David did the right thing in spite of discouraging insults and fearful threats. Only God's opinion mattered to David.