Purgatory revisited

Commenting on my post, Protestant defends doctrine of Purgatory, one of my students asked:

"I wander how the doctrine of purgatory in effect makes a separation between Justification and Salvation, one being "sola gratia" and the other via Sanctification?"

It may be true that Catholic doctrine generally does not effect any separation between justification (as imputational) and sanctification (as actual), or between divine prevenient grace and human obedience. St. Augustine says:

"He who made you without you, will not justify you without you." (Sermons 160.13)

Yet this answer may not adequately address Protestant concerns. It may be helpful that Augustine also wrote this:

"God, when crowning our merits, crowns nothing else but His own gifts to us." (Letter to Sixtus, 45; AD 418)

But what those from Protestant backgrounds are often concerned about is the impression that Catholic doctrines, like Purgatory or Penance, can sometimes give that human beings by their own merits independently of God's prevenient grace are somehow expected to atone for or otherwise pay for their own sins and to some extent thereby earn their passage to heaven under their own steam, as it were.

Peter Kreeft has the gift of simplifying matters, even if on some occasion he may verge towards the precipice (with its concomitant hazards) of oversimplification. Here, though, he may be helpful. In his book Everything You Ever Wanted to Know About Heaven, but Never Dreamed of Asking (San Francisco: Ignatius Press, 1990), pp. 62f., he says that Purgatory is:

1. part of Heaven, not a distinct, third place between Heaven and Hell--thus the absolute antithesis between Heaven and Hell, and its infinite spiritual seriousness, is preserved;
2. joyful, not gloomy--thus not detracting from the joy and triumph of Christian death (in fact, one of the saints [St. Catherine of Genoa, in her treatise on Purgatory] even says that the pains of Purgatory are incomparably more desirable than the most ecstatic pleasures on earth!);
3. a place of sanctification, not justification, where sin is not paid for (that was completed on Calvary) but surgically removed. As George MacDonald says, He was called Jesus not because He was to save us from punishment merely, but because He was to save us from our sins;
4. Purgatory is also a place of spiritual education rather than deeds; thus it is not a "second chance" to pay for sin or merit salvation, but a full understanding of deeds already done during our first and only chace, and a full disposal of all that needs to be disposed.

Protestants are often surprised that C.S. Lewis affirmed the existence of Purgatory:

Our souls demand Purgatory, don't they? Would it not break the heart of God said to us, "It is true, my son, that your breath smells and your rags drip with mud and slime, but we are charitable here and not one will upbraid you with these things, nor draw away from you. Enter into the joy"? Should we not reply, "With submission, Sir, and if there is no objection, I'd rather be cleansed first." "It may hurt, you know."--"Even so, Sir." (C.S. Lewis, Letters to Malcolm: Chiefly on Prayer (New York: Harcourt, Brace, Jovanovich, 1973), pp. 108-9.)