Albert Barnes Commentary Psalms 139:1

"O Jehovah, thou hast searched me, and known [me]." — Psalms 139:1 (ASV)

O Lord, you have searched me - The word rendered 'searched' has a primary reference to searching the earth by boring or digging, as for water or metals. See Job 28:3. Then it means to search accurately or closely.

And known me - As the result of that search, or that close investigation. You see all that is in my heart. Nothing is, or can be, concealed from you. It is with this deep consciousness that the psalm begins; and all that follows is but an expansion and application of this idea. It is of much advantage in suggesting right reflections on our own character to have this full consciousness: that God knows us altogether; that he sees all that is in our heart; and that he has been fully acquainted with our past life.