David was relentlessly pursued by King Saul because he was jealous that God had favored David in his place. In many instances, we find David fleeing from his enemies and begging the Lord to grant him salvation, vindicate him, answer his prayer, and rescue him from the violent men who sought to murder him. Perhaps this verse, David's statement of faith, summarizes the essence of this Psalm.
Faith is essential for pleasing God. An excellent example of a man demonstrating a growing faith in God is found in this short, simple Psalm. Instead of relying on his own abilities and strength, he places his trust in the Lord and is confident that God's Word will be fulfilled. God's Word is certain to him, and he is confident that God's promise of things to come will be fulfilled without failing.
David's trusting faith described in this Psalm is an example of the secure faith that each of us wishes to develop in our Christian lives. However, it is not easy to stand firm on God's promises when faced with difficulties and dangers. Regardless of the difficulties that may arise, let us put our trust in the Lord and stand firm in His promises.

Dear Heavenly Father, I praise and thank You for Your Word and the encouragement it gives. I learned from David, who stood firm on Your promises regardless of the evil, violent men who pursued him to destroy him during his time of trial. I praise You for being my God, my helper, and my sustainer. Please keep my feet on the path of righteousness, not letting the stresses and strains of life throw me off Your Word. 
In Jesus's name I pray. Amen.