David finds great relief in the Psalms today after God answers David’s prayers and saved David from his enemies, specifically Saul here, if we remember in the Bible, Saul really had it in for David, and Saul was literally chasing David all over Israel with the intend to kill David, David has been praying to God for deliverance from Saul, and God rescues David:  

Psa 18:1  For the choir director: A psalm of David, the servant of the LORD. He sang this song to the LORD on the day the LORD rescued him from all his enemies and from Saul. He sang: I love you, LORD; you are my strength.

Psa 18:2  The LORD is my rock, my fortress, and my savior; my God is my rock, in whom I find protection. He is my shield, the power that saves me, and my place of safety.

David puts all the onus on God here, likening God to his rock, fortress, savior, protector, noting that David doesn’t take any credit for eluding Saul, David puts all that on God, and then a great verse here that reminds us that God answers prayers: 

Psa 18:3  I called on the LORD, who is worthy of praise, and he saved me from my enemies.  

Lots of times when we have some great victory in life, we get foolish and want to pat ourselves on the back, David could have done that too thinking look how slick I was by getting one up on Saul, but David knows that the came at the divine hand of God, not his own faculties.  A great reminder here that God runs the show, everything that happens, both bad, and in this case; good, comes from God not man.