Confusing the two will bring condemnation and distance us from the Lord… but separating the two… perhaps just as bad.

Justification refers to my status; sanctification to my state.

Justification is about God’s attitude to me changing; sanctification is about God changing me.

Justification is about how God looks on me; sanctification is about what he does in me.

Justification is about Christ dying for my sins on the cross; sanctification is about Christ at work in me by the Holy Spirit changing my life.

The Reformers were careful to distinguish the two—but not to separate them. One cannot have the one without the other—as with the heat and light of the sun. The sun gives out heat and light. These two cannot be separated. When the sun shines there is both heat and light; yet they are distinct and not to be confused. We are not warmed by the sun’s light nor illuminated by its heat. To use a modern illustration, justification and sanctification are like the two legs of a pair of trousers, not like socks which may well become separated and, in the author’s experience, too often do become separated.

Anthony N. S. Lane from Justification by Faith in Catholic-Protestant Dialogue: An Evangelical Assessment