I know that nothing good lives in me, that is, in my sinful nature. For I have the desire to do what is good, but I cannot carry it out.
— Romans 7:18
As long as we live here on earth, we will have two natures—one foul, the other blest. The old nature is irreparably evil and corrupt. The only thing that can be done with it is to destroy it. It must be crucified with Christ, and a new nature must replace the old. While the old nature diminishes, the new nature grows.
Remember, the old nature cannot be improved; it has to be removed. It can’t be mended, therefore it must be ended. Only Christ can do that. He does it by the continual supply of His grace. Having come to live in our hearts, He continually supplies His grace, so that we can grow in that grace. It is all done by Christ; it is all done by the work of His Holy Spirit in our hearts.
When we ask God to slay us, it is not a prayer of destruction, but rather a prayer of reconstruction. We are asking the Lord to slay our sinful nature and to put to death all that is opposed to Him and all that hinders our new nature and steals our peace. It is because of our trust in God’s goodness that we can pray this prayer, “Slay me.”