David is a badass.The same God that empowered David, kings and other great leaders is in me. I have the same authority in Christ to overcome any sort of trouble that happens in my life. The fear of man is one fear I should never have if I truly believe I belong to the same God that saved Israel over and over and over again.
At the point, David was just a boy who watched over sheep all day. There was nothing cool or flashy about that job. But David knew who his LORD was and the power He gave to those who were after His heart. He says it perfectly in verses 34-37:
"Your servant has been keeping his father's sheep. When a lion or a bear came and carried off a sheep from the flock, I went after it, struck it and rescued the sheep from its mouth. When it turned on me, I seized it by its hair, struck it and killed it. Your servant has killed both the lion and the bear; this uncircumcised Philistine will be like one of them, because he has defied the armies of the living God. The LORD who rescued me from the paw of the lion and the paw of the bear will rescue me from the hand of this Philistine."
The best part about David was his life was a mess. He screwed up multiple times and did some serious damage. Fortunately, when we come to God and admit our crap... He has already forgotten it and wants us to continue to pursue Him. He doesn't want to put guilt on us or shame... that is what Satan does. I knew someone that once told me that every time he read his bible he felt guilty, so he stopped reading it. That isn't God putting guilt on him, that is Satan lying to him and telling him he isn't ever going to be good enough for God's love. God wants all who are weak to come to him so He can build us up and make us strong. Jesus didn't go to those who had it all together... I believe this is why we need to surround ourselves with a community of people who know they aren't perfect and are in desperate need of God.
The hardest thing to let go of is our pride and to humbly come before the Lord asking for help. But it's not until we do that when we then gain strength like David to overcome the "giants" in our life.