To start, we must see that justification and sanctification are linked, are not to be severed from each other. The Bible is clear that those whom God justifies, he also sanctifies ( 1 Corinthians 1:30). Both justification and sanctification are fruits of our union with Christ. Because we are ‘in Him’, we are justified. On the flip side, because we are ‘in him’, we are also being sanctified.
Yet, justification and sanctification are also distinct. Here are three ways in which justification and sanctification are distinct from each other. These are taken directly from Anthony Hoekema's 'Saved By Grace'.
a) Justification removes the guilt of sin, whereas sanctification removes the pollution of sin and enables the believer to grow in his or her likeness to Christ.
b) Justification takes place outside the believer and is a declaration made by God the Father about ones legal status. Sanctification, however, takes place within the believer and progressively renews his or her nature.c) Justification takes place once for all and is neither a process nor a repeated event. Sanctification, however, as it is usually understood, is a process which continues throughout life and is not completed until after this life is over.