Here's an odd way of looking at sanctification.
First, a decent summary of the distinctions between the two great Biblical doctrines of justification and sanctification:
Justification is God's declaration that a sinner is righteous through the work of Jesus Christ.
Sanctification is God's transformation of a believer's whole being, that is the mind, will, behaviors, and affections through the work of the Holy Spirit.
So, here's my take, based on these final verses in Galatians, on sanctification. Sanctification is not primarily an awareness of how good we are becoming. Instead, it is primarily a growing sense of how sinful we really are, and so how we need constantly to turn to and depend on Jesus.
Paul has spent this entire letter maturing us to seeing the truth of that