Many there be which say of my soul, There is no help for him in God. Selah.
 But thou, O LORD, art a shield for me; my glory, and the lifter up of mine head.
 I cried unto the LORD with my voice, and he heard me out of his holy hill. Selah.
3:1,2 Many: The main antagonist in David's life at this time was his son, Absalom. Unfortunately, David's friends had also become his foes because they were advising him that no one would come to his rescue, not even God. Selah: This simply means to pause and think about what was said. It is a musical term and it frequently used throughout this book of Psalms.
3:3,4: The word but shows contrast. The mood of the Psalm is changed from rejection to rejoicing. The Psalmist David says three things of the Lord: (1) When no one would help David, God was his shield. (2) When David had nothing to treasure, God was his glory. (3) When no one would encourage him, God Himself would encourage him and lift up his head. God did not turn a deaf ear to his child. He heard him in time of need.