Great question? Why is it in your Bible? It's clearly all about David and some problem he was facing. Then why is it in your Bible? That's a great question too! We certainly already believe in God so we don't need to know about how powerful God is. What is the reason for this Psalm? Simply put it was personal for David because it's personal for YOU TOO! We are all but ignorant if we do not take on this Psalm 18 and use it for ourselves. Simple study would understand David as King of Israel sent this Psalm over to the choir director to be sung at least weekly if not daily for everyone to hear around Jerusalem. For it to be exclusively for David personally it would never have been made a Psalm. How many times have we all heard "the Psalms are not for us today"? Incredible unbelief we surround ourselves with every day. With that kind of thinking then we need to toss out the 23rd Psalm as well, and that would be absurd. Well, then tossing out the 18th is just as absurd. Every word in Psalm 18 can be depended on. Recognize your own unbelief and begin to take God at His word and believe Him to respond to you just like He did for David in this wonderful Psalm. Is there any wonder David killed Goliath thinking like he did here in this Psalm.