Psalm 139, presented to the chief musician of the temple choir, would have been set to music for singing in the temple service, as well as used in private worship by individual Israelites. 

It is believed by Biblical scholars that David was the writer. Verse 1 "O Lord, Thou hast searched me, and known me." KJV These words also apply to each of us today. 

The verbs here, searched and known, are in past tense.  The Hebrew word for search means to penetrate, to examine intimately. The verbs, linked to our divine God, opens our eyes to a truth of our God that may be difficult for us to grasp; this truth even escapes us. 

When we are having thoughts in our hearts and mind, deep within our soul, whether it be in the night when sleep is escaping, or in the daytime, when we may be secluded, deep in thought, every thought is searched by Him. 

If the thoughts are leading to action, He is even aware of our actions beforehand. The word searched, in past tense, refers to that not one of our thoughts or actions escapes God. The words confirm the deep-in-depth knowledge He has of us, therefore we are known by Him, and His knowledge of us is past, present and future of us..