Question: "Why did David choose five smooth stones before going to fight Goliath?

Question: "Why did David choose five smooth
stones before going to fight Goliath? Was David doubting God? Was it because Goliath had five brothers? Or, was David simply being
prepared?"
Answer: Some presume that David took five
smooth stones instead of just one because he
had some doubt. However, there is no indication
in the story of David and Goliath that by picking
up five smooth stones instead of one that David
was doubting God. Rather, David was simply
being prepared. What if the Philistines attacked
him after he killed Goliath? How would he have
defended himself? David was simply being
prepared when he took the four additional
stones. Also, he couldn’t have known that one
stone would be enough to kill the giant. God
had not promised that David would kill Goliath
with the first stone.
David had experience in defending the sheep he
guarded with his sling and stones. It would
seem that the animals David had faced were far
braver than the men with Goliath, because they
all turned and ran away ( 1 Samuel 17:51 ). David
told Goliath that he (Goliath) came with spear
and sword, but his weapon was God the Father
( 1 Samuel 17:37 ). He trusted God with all his
heart, believing that God would tell him exactly
what to do and how. And so He did.
Others speculate that David chose five smooth
stones because Goliath had four brothers, and
David was readying himself to dispatch all five
giants. This theory is based on 2 Samuel 21:15–
22. That passage lists four very large Philistines
who were related to Goliath in some way: Ishbi-
benob, Saph, Goliath, and an unnamed giant
with six fingers on each hand and six toes on
each foot. “These four were born to the giant in
Gath, and they fell by the hand of David and by
the hand of his servants” ( 2 Samuel 21:22 ). The
account of 1 Samuel 17 does not suggest that
David knew about Goliath’s brothers or that he
believed he would have to fight the whole
family. What we know for sure is that David and
his men faced four other giants, somehow
related to Goliath, in later battles.
David’s faith was in the Lord, and he knew from
experience God’s faithfulness. David’s faith was
born out of his experience of God’s grace and
mercy in his life up to that point. The Lord had
delivered him out of dangerous situations in the
past, proving His power and trustworthiness,
and David relied on Him to deliver him from the
Philistine. Whether it took one stone or five,
David recognized that the power was not in his
sling but in the Lord of hosts. As David wrote
later in Psalm 21:13 , “Be exalted, O LORD, in
your strength; we will sing and praise your
might.”