Psalms 18-19: You're My Rock

It is impossible that the words of our heart and especially the meditation of our hearts be pleasing to God unless we totally rely on him as our rock.

David knew that.  He knew that God strengthened him.  He knew that he was wholly dependent on him.  He knew he was lost without God in his life, and with him, there was nothing that could stand against him.  He knew that God was perfect, in every aspect.

As for God, his way is perfect; the word of the LORD is flawless.
He is a shield for all who take refuge in him.
For who is God besides the LORD ? And who is the Rock except our God?
It is God who arms me with strength and makes my way perfect.
He makes my feet like the feet of a deer; he enables me to stand on the heights.
He trains my hands for battle; my arms can bend a bow of bronze.
You give me your shield of victory, and your right hand sustains me;
you stoop down to make me great. - Psalms 18:30-35 - NIV

The only thing that David couldn't know or see, although perhaps his words in this psalm foretell it, is just how far God would stoop down to make us great.  None of the ancients could see, except as through a glass darkly, the extent of God's love for his creation.  They did not know that he loved us enough that he sent his only son that we might be saved.  They did not know that those outside the chosen children of God could be grafted in and become children of God as well, because of his great love and the sacrifice of his son.