"Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ"   (I Thess. 5:23).

Paul is encouraging us to make godly decisions to let the Lord Jesus Christ really be Lord in all things in life.  Our sanctification certainly is the will of God (I Thess. 4:3).  This is a learning  process for Paul tells us, "that each of  you  should know how to possess his own vessel in sanctification and honor" (I Thess. 4:4).  The key thing to realize and know is that we must have the Lord as our source for all things in this process if genuine sanctification is going to happen.

First, Paul tells us that the God of peace Himself is going to sanctify us completely (I Thess. 5:23a).  Does that leave out anything there?    No, that means that the God of peace is a part of all sanctification.  When we heard the word of salvation in the beginning, and simply believed by faith (Rom. 10:9-10), the Holy Spirit birthed us again (I Pet. 1:23).  We received Christ and a new nature and spirit to now live inside us (Gal. 2:20; II  Pet. 1:4).  That made us complete  in Spirit, with all the fullness of Christ in us (Col. 2:10).  For the first time we have unity  in Spirit (I Cor. 6:17) and we have His sanctification in Spirit (I Cor. 1:30).   This speaks our positional sanctification with the Father that is complete, for our relationship to begin a new life of fellowship in the Spirit.

Ah, but we still have the same mind that has not been fully renewed by the Holy Spirit.  This is a continual process that must ever take place throughout life.  This speaks of our  practical sanctification in soul and body.  We will need to fully cooperate with the Holy Spirit and allow Him to renew our minds to Jesus Christ and Him crucified (I Cor. 2:2).  As long as we live in our unrenewed or fleshly mind we will not be fully allowing Christ to express His sanctified life within us.   A Holy Spirit renewed mind, that chooses to let Christ have full expression in and through us, is the only genuine sanctification within us.