In Psalm 3 we cactch a glimpse of David as he is overwhelmed by foes surrounding him, foes both of his own household and those without decrying owe and ill. In verse 3 David says, "But you, Oh Lord, are a shield about me, my glory, and the lifter of my head." He cried aloud to the Lord hoping—in his wearying faith—that these things might me true. Hoping that he will be given the faith to believe more fully. Hoping that God will display His truthfulness at the appropriate time. And then David went to sleep, "I lay down and slept" (verse 5). It's amazing what rest can do to disambiguate an overwhelming situation. Rest for the body. Rest for the soul. Rest for the mind. Rest in the One Who made us and in Whom we are hoping. God can use rest—that time when we actually dispare of our own competency, our own strength—to renew us body, mind, and soul. And in this rest God bestows on us, just as He did to David, the courage a new start and a new day has to offer. "I woke again, for the Lord sustained me. I will not be afraid..." (verses 5-6). David's hope and expectancy is brought to fruition and faith is renewed. Not only does David truely believe once again in God's promises, but now he has been given the faith and strength to live like it, "Strength belongs to the Lord; your blessing be on your people" (verse 8).
1 O Lord, how many are my foes!
Many are rising against me;
2 many are saying of my soul,
there is no salvation for him in God. Selah 
3 But you, O Lord, are a shield about me,
my glory, and the lifter of my head.
4 I cried aloud to the Lord,
and he answered me from his holy hill. Selah
5 I lay down and slept;
I woke again, for the Lord sustained me.
6 I will not be afraid of many thousands of people
who have set themselves against me all around.
7 Arise, O Lord!
Save me, O my God!
For you strike all my enemies on the cheek;
you break the teeth of the wicked.
8 Salvation belongs to the Lord;
your blessing be on your people! Selah