Psalm 3

The Story of David
From the "New Jo Version" (NJV) 

Imagine coming from a giant family where no one really cared for you all that much.  Then God said you would be king, which is cool and all, but you never asked for it, and then the current king started chasing you around everywhere trying to kill you.  After a ton of heartbreak and annoyance and perseverance, you finally become king, just as God said.

Everything is going well, just as it should be.  Then you made this awful mistake where you coerced a married woman into sleeping with you and then killed her husband because she got pregnant.  The kid dies, and you do the only decent thing a king can do in that time period- you marry the woman and stick her together with all your other wives.  You feel awful and repent.  But even though you think you've sufficiently learned from your mistakes (you're a man after God's own heart, after all, despite your faults) it turns out that you've set into place an even worse set events that ends up in your son raping your daughter and another son getting mad, chasing you around, and trying to kill you.  (You're a classic case of High "Spirituality" Does Not Translate Into Good Family Man.)

Remember how God said you'd be king?  That peace is broken.  You screwed it up.  And now someone's chasing you around trying to kill you.  Again.  Bummer.  You've made some Really Awful Mistakes and now you're facing the consequences.

And yet- God sustains you.  He protects you from your enemies.  You probably deserve what's coming...but it never comes.  Because God has more in store for you.  He has placed you on the throne, and He's going to keep you there.  He has a plan for you that's bigger than you.  God's kindness does not make you proud, it makes you humble.  You aren't saved because you're cool and awesome- salvation belongs to God and God alone.  You praise Him for it.  And though enemies swarm you, you are not afraid.  You lay down and sleep.  You call out to God, and He sustains you.

So look to God for salvation, trust him, and sleep.