…justification removes the guilt of sin; sanctification removes the pollution of sin and renews us in the image of God.
And therefore, last, by definition justification is a once-and-for-all act. It is never to be repeated because it cannot be repeated and never needs to be repeated. It is not a process but a declaration that we are pronounced just once and forever, by God. Sanctification, on the other hand, is a continuous process. We continue to grow in grace and in the knowledge of the Lord until we are perfect beyond the veil.
Martyn Lloyd-Jones and Robert Backhouse, Walking with God Day by Day: 365 Daily Devotional Selections, (Wheaton, IL: Crossway, 2013).