The Holy Spirit carries out both offices together: He slays and makes alive...

The Law indeed says it is God's will and command that we should walk in a new life.  But it does not give the power and ability to begin and to do it.  The Holy Spirit renews the heart.  He is given and received, not through the Law, but through the preaching of the Gospel.  Thereafter, the Holy Spirit uses the Law in order to teach the regenerate from it and to point out and show them in the Ten Commandments what is the "will of God, what is good and acceptable and perfect" (Romans 12:2) in what "good works, which God prepared beforehand, that we should walk" (Ephesians 2:10).  He encourages them  to this.  When they are idle, negligent and rebellious in this mater because of the flesh, He rebukes them through the Law.  So the Spirit carries out both offices together: He slays and makes alive.  He leads into hell and brings up again.  For His office is not only to comfort, but also to rebuke.  For it is written, "when [the Holy Spirit] comes, He will convict the world [which includes also the old Adam] concerning sin and righteousness and judgment" (John 16:8).  Sin is everything that is contrary to God's Law.  St. Paul says, "All Scripture is breathed out by God and profitable for teaching, for reproof" (2 Timothy 3:16), and to rebuke is the Law's special office.  Therefore, as often as believers stumble, they are rebuked by the Holy Spirit from the Law.  By the same Spirit they are raised up and comforted again with the preaching of the Holy Gospel.
~BOC, FSD, VI, 11-14