The story Jesus tells in Luke 18 is not just about justification and how one can be justified (v. 14). It’s also about pride and humility; and Jesus’ purpose in telling the story is to expose the pride of the self-righteous Pharisees (v. 9). And that means this is a parable not only for unbelievers, to expose their sinfulness, but it is also a parable for believers to expose the pride in their hearts.
The justified man is a humble man; the self-righteous (unjustified) man is the prideful man. So even in believers, to the degree that pride controls us, we are living as unjustified men.
So here is a chart of this parable that can serve as a self-examining test. What are the activities of my life — am I proud or humble?