For forty days the Philistine came forward every morning and evening and took his stand

1 Samuel 17:1-37
 The Philistines occupied one hill and the Israelites another, with the valley between them.
Goliath stood and shouted to the ranks of Israel, “Why do you come out and line up for battle? Am I not a Philistine, and are you not the servants of Saul? Choose a man and have him come down to me.
On hearing the Philistine’s words, Saul and all the Israelites were dismayed and terrified.
For forty days the Philistine came forward every morning and evening and took his stand.
Now Jesse said to his son David, “Take this ephah of roasted grain and these ten loaves of bread for your brothers and hurry to their camp.
The Philistine champion is 10 Ft(over 3 meters) tall, fully armed and clad in protective armor. Saul, who has fought valiantly against the Philistines, is as terrified as his men to answer the giant's challenge. 
Why?
Everyone faces Giant enemy is fear and dismay, for we are weak and small.
Forty days, Goliah and Philistian came out shouted to Israelite. This is the number of the Lord. Waiting for God's way to be done. Jesse asked David took grain and bread for his brothers, so he has the opportunity to meet the great war.
How?
God has his time and way and the right person to do his mission. For us, waiting for God's leading, focus on the Lord and follow his word, trust in the Lord. I am God's servant.