David was physically and mentally ill, deeply distressed, and spiritually depleted due to the mounting pressures and numerous enemies surrounding him on all sides. In spite of this, David expressed great confidence in the fact that his cries had been heard by God. David's experience should serve as an encouragement to all believers. His prayer was answered by the same Lord who promises to answer ours as well.
When David focused on the enemy and the gravity of his situation, his strength was sapped. However, as soon as he refocused his heart on the Lord and remembered God's many precious promises, he was able to pray effectively with thanksgiving and praise. David came to understand that God was with him throughout all of his trials and tribulations and that his prayer had been heard and answered.
Like David, when we are surrounded by our enemies, wounded physically, concerned mentally, and overwhelmed spiritually, we should remember the many precious promises of God. And let us never forget that in Him we have access to the heavenly throne of grace, through which we have access to mercy to find assistance in times of need. It is important, however, that we approach Him reverently, prayerfully, and confidently, knowing that He hears and answers our prayers.

Dear Heavenly Father, Thank You for listening to and answering my prayers. Thank You for providing me with all my needs in accordance with Your riches in glory. Instead of focusing on the circumstances of life, I pray that I may focus on Christ, my Life and my Healer, my Shield, and my Defender, my Hope and my Salvation. Please don't let me take Your precious promises for granted, but give You reverence and glory. 
In Jesus's name I pray. Amen.