Of course, the process [of sanctification] must culminate at some point, and there is no reason why it may not reach its end in an act of faith in this life, just as Wesley believed it could. But the significant point is that considerable growth is required before such a stage can be reached. And if this growth has not occurred in this life, purgatory seems necessary if God is to complete the job with our freedom intact.
These accounts of purgatory underscore the notion that no one can be exempted from the requirement of achieving perfect sanctity in cooperation with God’s grace and initiative. It is also important to reiterate here that, as beings who exist in time, our transformation must be a cooperative venture. It takes time to gain understanding of the various layers of our sinfulness and self–deception, as well as to own the truth about ourselves. Discerning truth and allowing it to transform our character is an essentially mental experience that requires time. The doctrine of purgatory makes clear that there is no shortcut to sanctity.
— Jerry L. Walls, “Purgatory for Everyone”