There are 3 levels or dimensions to salvation: The salvation of the spirit, the soul and the body. (1st Thessalonians 5:23)
Sanctification is the core principle of the salvation of the soul! (James 1:21)
Sanctification means accessing the grace of God to daily submit to the work of the Holy Spirit in conforming you to the image of Jesus Christ.
In every situation, everyday, you choose, as an act of your will and through the power of the Holy Ghost, to obey God rather than your flesh or the dictates of the world around you.
This is the process of sanctification.
In regeneration the Holy Spirit re-created your spirit in the image of God. In sanctification He is continuing this work by extending the process to your soul.
Regeneration transforms your nature
Sanctification transforms your character
Regeneration happens instantaneously - Sanctification takes a lifetime to complete.
Regeneration qualifies you to enter Heaven - Sanctification prepares you to rule on the New Earth. (1st Corinthians 15:50)
It is the same work of salvation but just moved to a different level. The work the Holy Spirit began in transforming your spirit is now continued in the transformation of your mind.
The soul and the mind are one and the same thing.