Albert Barnes Commentary Psalms 139:18

"If I should count them, they are more in number than the sand: When I awake, I am still with thee." — Psalms 139:18 (ASV)

If I should count them - If I could count them.

They are more in number than the sand - Numberless as the sand on the sea-shore.

When I awake, I am still with thee - When I am lost in deep and profound meditation on this subject, and am aroused again to consciousness, I find the same thing still true. My being forgetful, or lost in profound meditation, has made no difference to you. You are still the same; and the same unceasing care, the same thoughtfulness, still exists in regard to me.

Or, the meaning may be, whether I am sleeping or waking, it is still the same in regard to you. Your eyes never close. When mine are closed in sleep, you are round about me; when I awake from that unconscious state, I find the same thing existing still. I have been lost in forgetfulness of you in my slumbers; but you have not forgotten me. There has been no change—no slumbering—with you.