King David killed Goliath and led his armies to battle and returned with great victories.
But in all of their victories they realized that it was God who gave them the victory. It's summed up in verse 3.
3 It was not by their sword that they won the land, nor did their arm bring them victory; it was your right hand, your arm, and the light of your face, for you loved them.
Jeremiah gave this instruction which says the same thing in a little different way.
Jeremiah 9: 23 Thus says the LORD, "Let not a wise man boast of his wisdom, and let not the mighty man boast of his might, let not a rich man boast of his riches; 24 but let him who boasts boast of this, that he understands and knows Me, that I am the LORD who exercises lovingkindness, justice and righteousness on earth; for I delight in these things," declares the LORD.
What are you good at? Do you recognize that it is God who gives you that ability and any good things that come from it?
What difficulties are you facing? Do you realize that you don't have to rely on your own strength or cleverness or abilities? I'm not saying you shouldn't be prepared in life. I'm not saying that you shouldn't work hard. You should give every situation your best. The Israelites fought hard for the Promised Land. But it is God who brought the victory. It is God who will bring the victory in your life.
And here's my favorite part! Do you know why? Because of His love!
If you spend some time meditating on what it means to have the light of God's face working in your life - because of His love for you - it will change your life.
Bonus Bottom line:
If you can boast that you understand and know God then you will delight in what He delights in - exercising lovingkindness, justice and righteousness. Then you will also delight in (and do) those things.