The contest between David and Goliath was a life changing experience for the people who witnessed it. Work through the list of humans in the Valley of Elah that day to comprehend the magnitude of what happened as a result of a sling and one stone---
 the Philistine warrior Goliath was dramaticaly killed.
 the vast Philistine army fled the battlefield in shameful defeat.
 the Israeli army were victorious and plundered the Philistine encampment.
 King Saul retained his throne but eventually was consumed by jealousy of
David. He fell on his sword rather than be captured by the Philistines.  Jonathan, the king's son, was bound to David in a lasting friendship.  the brothers of David assumed lesser roles in the kingdom.
 The father of David, Jesse, was remembered in Scripture, eventually protected
by King Saul, and was mentioned in Isaiah 11, "the root of Jesse" as the line of
the coming Jewish Messiah, Jesus Christ, the Lord.
 David became armor bearer to the king, commander of the kings armies, and
was eventually anointed as king of Judah, later of the entire nation. He
defeated the Jebusites at Jerusalem and the city is known since as the "city of
David". Later God initiated the Davidic Covenant with David to insure the
kingship to his sons and continuance of his name. He also wrote most of the
Psalms, and even though sinful in many ways, is remembered in history as the
"man after God's won heart" (see 1 Samuel 13:14; Acts 13:22).
You see, David's victory over Goliath changed the lives of thousands, perhaps millions of people living in that geographical area and at that time. Of course, his influence is as profound today, and in every phase of human history since that day, because of his character, courage, and willingness to be God's vessel in critical times.
The most imposing lesson of the sling and five stones isn't about change, however. It isn't about how the status of the people involved that day was elevated or diminished by the result of the contest. Yes, there are many lessons taught about young David facing the giant Goliath. You know, preferred legends about underdogs, overcoming the odds, being outnumbered or out-manned. Who doesn't cheer for the little guys like Rocky Balboa, Rudy, and so many others. But, the David and Goliath epic isn't about these kind of heart rending stories, as much as we like to rehearse them.
It's not about what happens to winners and losers either, the changes that altered the lives of the humans on the playing field or in the stands. Underneath the layers of victory and defeat is a power lesson about the one unchanging reality of life---our faithful and unchanging God. It's a clear theme in the text. The historian wrote about the young shepherd boy David being questioned by King Saul before facing Goliath. The words are a thrilling revelation about God----
When the words that David spoke were heard, they repeated them before Saul, and he
sent for him. And David said to Saul, “Let no man's heart fail because of him. Your
servant will go and fight with this Philistine.” And Saul said to David, “You are not able to
go against this Philistine to fight with him, for you are but a youth, and he has been a
man of war from his youth.” But David said to Saul, “Your servant used to keep sheep for
his father. And when there came a lion, or a bear, and took a lamb from the flock, I went
after him and struck him and delivered it out of his mouth. And if he arose against me, I
caught him by his beard and struck him and killed him. Your servant has struck down
both lions and bears, and this uncircumcised Philistine shall be like one of them, for he
has defied the armies of the living God.” And David said, “The Lord who delivered me
from the paw of the lion and from the paw of the bear will deliver me from the hand of
this Philistine.” And Saul said to David, “Go, and the Lord be with you!”
1 Samuel 17: 31-37, ESV
Young shepherd boy David, long before leading the king's armies, long before defeating the tens of thousands, long before the Davidic covenant, intimately knew his Sovereign God. As King Saul and Israel were frozen in fear by the taunting giant warrior, this young shepherd boy knew that the God who had strengthened him against bears and lions would give him what was necessary to defeat this bombastic Philistine. The God who had given him courage, wisdom, and knowledge to defend his father's sheep would guide him against Goliath. He knew the unchanging God.
Life in exponential times changes at greater speed than any time in history. Change today is complex and fast. We need to know the God that David knew so intimately, the unchanging God. This truth is central to God's faithfulness in history. God spoke it to the prophet Malachi---"For I the Lord do not change; therefore you, O children of Jacob, are not consumed" (Malachi 3:6, ESV). Good old practical James affirmed this truth when he wrote, "Every good gift and every perfect gift is from above, coming down from the Father of lights with whom there is no variation or shadow due to change" (James 1: 17, ESV). Many other Scriptures remind us that the God who guided David is the God who is Sovereign over all things at all times, even the minute things of our daily lives today.
Change? Yes, it is real. But, David knew the unchanging one. This God is the ultimate lesson learned from that youthful shepherd boy. Five stones and a sling? Yes, believe it.