I read a story about a group of children that “was lining up for lunch in the cafeteria of a church primary school. At the head of the table was a bowl of juicy apples. The supervising nun wrote a note and placed it next to the apples: ‘Take only ONE. God is watching.’ At the other end of the table was a large pile of chocolate coated biscuits. A child had written a note and put it next to the plate: ‘Take as many as you want. God is watching the apples.’”
In v. 1, David asks the LORD for preservation and protection. He asks the LORD to watch over him.
In v. 9, David says that he rejoices in his whole being. His physical life is secure. The reason is in v. 10—God will not bring him to Sheol—the place of the dead. God will not let him die and see physical corruption. I think v. 1 and v. 9 are connected. To be preserved by the LORD for David is to be protected from physical corruption.
David is not saying here that he rejoices because God will save him from death. Rather, David is saying that he rejoices because God will not let him die yet. Because if God will not let him die yet, he will still enjoy the presence of God.
In v. 8, he just finished saying that the LORD is at his side. Because the LORD is at his right hand, therefore, he will rejoice. He will rejoice because he will not yet suffer physical death. Why would David rejoice for not suffering death? The reason is that death will end his enjoyment of the presence of God.
In the worldview of the Psalms, death is not just the end of life.Death is to be cut off from the presence of God. Death is detachment from the pleasures of the presence of God. Death is a cessation from enjoying the presence of God. Death is a termination of praising God. Death is the loss of the memory and act of praising God (Ps. 6).
To the psalmist, then, you do not only lose your life in death. In death, you lose God Himself. That is why David rejoices that he will not yet die. Because to die is to lose God Himself.
Thus, David rejoices because while still living, he will still enjoy the pleasures of the presence of God. He will not lose God.
 “Sermon Illustrations: God – His Nature, Attributes And Power.” Cited December 1, 2012. Online: http://hotsermons.com/sermon-illustrations/sermon-illustrations-god.html
 Mays, Psalms, 87.