Charles H. Spurgeon on Psalms 139:1

O LORD, thou hast searched me, and known me. David here lays down the great doctrine, that God has a perfect knowledge of us, First, in the way of an address to God: he saith it to him, acknowledging it to him, and giving him the glory of it. Divine truths look full as well when they are prayed over as when they are preached over: and much better than when they are disputed over. When we speak of God to him himself, we find ourselves concerned to speak with the utmost degree both of sincerity and reverence, which will be likely to make the impressions the deeper. Secondly, he lays it down in a way of application to himself: not thou hast known all, but "thou hast known me"; that is it which I am most concerned to believe, and which it will be most profitable for me to consider. Then we know things for our good when we know them for ourselves. Job 5:27 ... David was a king, and "the hearts of kings are unsearchable" to their subjects (Pr 25:3), but they are not so to their sovereign. —Matthew Henry.