David’s Song (also recorded as Psalm 18) is first and foremost a prophesy of the coming Messiah, as it says things which cannot be said of any ordinary man.
However, it is also a summary and reflection of the life of David, who sang this song “in the day that the LORD delivered him from the hand of all his enemies and from the hand of Saul.” And thus we consider the great drama of the life of David with it’s many ups and downs, and see how through it all, David was faithful to the LORD (despite his many sins and shortcomings), and the LORD rewarded David and delivered him from his enemies.
All of this serves to place David as a witness for us to the faithfulness of God. Why should we believe this prophesy of a faithful Messiah who is delivered from His enemies…? Because David was a faithful man whom God delivered from his enemies.
David’s life is the perfect testament to the faithfulness of God towards those who serve Him