Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
Psalm 139 shows the complete exercise of heart that belongs to God's ways. Though the faithfulness of God perfects all His purposed blessing, not a thought escapes God. There is, morally speaking, no staying in His presence; but there is no getting out of His presence, nor where He sees not, though conscience might be glad to flee. But this brings in another aspect. He knows all, because also He has formed all. This connects us with the taking perfect notice of us in goodness. He cares for us, watches over every member that is formed, as He knows our every thought; if He does, He has His own too, and these are precious to us. This is just the change and working of faith. It begins necessarily by conscience under God's eye; for it brings us into His presence, and then gets at God's thoughts, who has formed us for Himself, and then unfolded boundless spheres of His own blessing and ways. God watches over him in the silence of sleep: waking, therefore, he finds himself with God.
But, further, this connection with God is a perfect breaking with the wicked: God will slay them. And he calls on them to depart from him. Therefore he looks at the wicked with horror, because of what they are to Godfor himself, that he may be searched throughout, that no wickedness may remain in him. This psalm goes far in the relationship of man's spirit with God, though it looks to the external judgment of the wicked and uses language which becomes verified in the assembly figuratively, and which is so also in the resurrection. The great direct point in it is the full searching out of man's heart, as it will be then, as it must be ever. But this searching, when we are under our own responsibility, is, Whither shall I flee from Him? But when we are God's workmanship (that is, when grace and power have come in), God's thoughts become precious to us, and we can ask to be searched, known, and triedthe more the better, that, emptied of self, we may be able to enjoy God. Then also we look for leading. The will is broken, as the thoughts are judged, and our desire is to be led of God. We see at the same time the character of the psalm connects it with the latter day. "Surely thou wilt slay the wicked." It looks for judgment, and has hatred and horror of the haters of God.