The Apostle says in 1 Cor 5 7Get rid of the old yeast that you may be a new batch without yeast - as you really are. For Christ, our Passover lamb, has been sacrificed."
The apostle is carefully teaching we are established completely by the accomplished work of Christ. Our continual struggle is not primarily having acute tension with the cruel world or our personal corruption but becoming familiar in our identity with Christ. The unique means by which we can become secure in our identity is by sacred word and Spirit. David is fittingly describing the discipline of finding all of our mutual satisfaction and security in Christ by daily meditation. We grow by thinking thoughts after God. Learning to trust in the literal teaching of the well-worn Bible and comparing all the pernicious counsel of this world with the bible.

 David is teaching we are naturally the incompetent trusting in our untaught perspective of the events in our lives. We must progressively develop the lifelong habit of distrusting the prosecuting counsel of this delusional world by a mutual fear of acting without first thinking about it as we meditate. Psalm 139 represents the comprehensive philosophy that David has developed by many hours of meditation.The words adequately express the enjoyment of a man who is fulfilled by the valuable counsel of God that has been etched in His minds through meditation. Psalm 139 is the ultimate fulfillment of David as he has overcome the opposition in carefully examining everything in his life through Gods word.

He is teaching that without the discipline of meditation he would support social perspectives that steer him in a negative way that include acute sorrow. You see the problem is not we gain knowledge to recognize the shrewdest thing to perform. But we develop our love for God in the power of the Spirit to overcome our attraction to anything that would weigh us down. David is teaching the Christian life is primarily casting off things that are pleasing to us. They bear us back from finding all of our satisfaction in God.5 You hem me in-behind and before.  

Without the means of faith, we are incapable to cast off the weight of the pleasing things in this world. We all are searching for genuine satisfaction. The harsh world merely offers us emotional satisfaction that is limited and fleeting. The problem is we think we are capable of shielding ourselves from the enjoyment of that thing that will not satisfy us. The truth is we are secure in our instinctive desires with being controlled by something. We must promptly break with that cultural habit. Because Christ has developed us free of the control of things. It takes more than a warning to break off the relationship. We must be renewed in the spirit of our minds. Our discipline of meditation must ferry us to a place of freedom in Christ that is so much better that we have no desire to be suppressed. We must be experienced in pouring out our hearts with freedom as David expressed in 139. Consequently, we ask for God to hem us in from the temptations that are extremely strong for us. We must meditate on His counsel as the sole way to examine all things.