What lessons does the story of David and Goliath teach us?

It teaches us that God can accomplish the impossible, even when the vessels He uses are not really that impressive.

Also, Jeff, what did Barbados just say about not smart-alecky answers?

Don't mess with little guys?

The battle belongs to the LORD. 

1 Samuel 17:47 KJV — And all this assembly shall know that the LORD saveth not with sword and spear: for the battle is the LORD'S, and he will give you into our hands.

Psalm 24:8 KJV — Who is this King of glory? The LORD strong and mighty, the LORD mighty in battle.

https://youtu.be/c7uRX4srnsM

The story of David and Goliath is not about Jesus. It's a Jewish story from centuries before Jesus was born. 

The fact of the matter: It teaches us that if we have God by our side, we can do anything, as long as we keep God first in everything we do, God is the head of everything and we are his creatures and when we do God will then we will be blessed by God, and when we don't then we will be cursed by God.

It teaches us to let the Lord fight our battles.  As for heaven and hell, here is the truth: The Lord Jesus Christ is God. Nobody can be good enough to avoid hell. The truth is that death leads to immediate heaven or hell, depending only on whether the person believed on the Lord Jesus Christ, or not. The truth is that the Lord Jesus Christ loves you and wants to bless your life freely :) Most of all, Jesus wants you with Him forever, and not in hell. It is too late to be saved, after death.

.

Believing on the Lord Jesus Christ means being forgiven all sins past and future and means going to heaven. The truth is that every belief except one will lead to eternal torment in the lake of fire for every person. Because nothing pays for our sins except the death and blood of Jesus, the sacrifice of Jesus that is already accomplished by Him . Jesus loves you! The truth is that the Lord Jesus Christ is God, and Jesus died on the cross to pay for all of our sins in full, and then Jesus was buried, and then Jesus resurrected from the dead. Nothing else pays for our sins, not works, not deeds, not religions. So the only way to heaven and to avoid hell, is by believing on Jesus for eternal life (John 6:47), without adding any of your own works (Romans 4:5). Believe in the Lord Jesus Christ to take you to heaven, and you will be in heaven, no matter what, guaranteed. That easy, thanks to Jesus! Tell Jesus that you thank Him that you will be with Him in heaven

It teaches us that artillery and firearms and ranged or shooting weapons are superior to melee or hand to hand combat weapons. 

Historically the story does fall in line with the Israelites and nomadic tribes historically maintaining irregular units that likely used slings. If you want to see the damage a sponge can do you can just look it up on YouTube.  

This will get you started.

https://m.youtube.com/watch?v=_1oeZQH4oEc

Note- not all of the Bible’s stories are religious based much of it can describe the culture and times of an ancient people. The issues often with this are piecing it together with modern anthropology finds to verify and add fine tune it.

Writers don’t write in a vacuum. Those writers writing or contributing stories to the Bible would have done so in the cultural norms and practices of their times. In that regard the Bible is a window into the cutltural practices of ancient word much the same as reading a Japanese book from the 1900s or a Scandinavian book from the 1850s is or even just flat out reading Mark Twain is.

The bigger they are the harder they fall.

The story teaches us That Stop Motion Talking dogs and their errant masters can teach morals to Episcopalians on sunday mornings. 

WITH GOD WITH US WHO CAN BE AGAINST US??

And the Lord commanded to Go Lieth . Romans 3/7 for skydaddys' glory