1 Samuel 17:44-47
New King James Version (NKJV)
44 And the Philistine said to David, “Come to me, and I will give your flesh to the birds of the air and the beasts of the field!”
45 Then David said to the Philistine, “You come to me with a sword, with a spear, and with a javelin. But I come to you in the name of the Lord of hosts, the God of the armies of Israel, whom you have defied. 46 This day the Lord will deliver you into my hand, and I will strike you and take your head from you. And this day I will give the carcasses of the camp of the Philistines to the birds of the air and the wild beasts of the earth, that all the earth may know that there is a God in Israel. 47 Then all this assembly shall know that the Lord does not save with sword and spear; for the battle is the Lord’s, and He will give you into our hands.”
I don't think it's possible to get through life without facing a giant or two, or three, or four and even more. When I'd rather run away from giants and often try to do so, I need to remember that each giant is another chance to let the earth know there is a God in Israel. That's reason enough to fill a sling with stones and stride out into the battlefield.
Until the whole world knows...