There is no escape from His presence.
Whither shall I go from thy spirit? or whither shall I flee from thy presence? If I ascend up into heaven, thou art there: if I make my bed in hell, behold, thou art there. (Psalms 139:7-8 KJV)
David was contemplating about the ever-present presence of God. He realized that there was no place available to escape from Him. God exists, unlike mankind, seeing and discerning everywhere all at the same time. God can take in a wide view of heaven, hell, and this world from His perfect and infinite spiritual vision.
David understood as he was present in this world, in to come heaven, or for others who choose to go to hell God’s presence would be apparent; leaving no place to hide from His omnipresence or all-knowing spirit. Certainly David also understood that God will be seated upon the throne in Heaven for all eternity but He can view the eternal realm in Hell where those who did not place faith in God will be in the agonizing in flames forever.