What does Psalm 16:8 mean?

Here, David testifies that he trusts in the Lord to protect and defend him. In ancient writing, the "right hand" represented someone's ultimate strength and power. In the case of David, the sense that God was at his right hand was a feeling of confidence.

Along the same lines, David has identified the Lord as his guide (Psalm 16:7), now he identifies God as his guard. Having the Lord as a protection kept David confident and unafraid. Nothing would move or shake him. He was secure in all the blessings the Lord had bestowed on him. This goes beyond a shallow assumption that David will survive—as the following passage shows, this is a confidence that God is eternally with David even if he meets death (Psalm 16:9–11).

In John 10:28–29 Jesus promises to safeguard all who trust in Him. He says, "I give them eternal life, and they will never perish, and no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand." David knew that even if he walked through the valley of the shadow of death he did not have to fear because the Lord, his Shepherd, would protect him (Psalm 23:4).