"Here is a secret I will make known to you; we shall all rise again, but not all of us will undergo the change I speak of. It will happen in a moment, in the twinkling of an eye, when the last trumpet sounds; the trumpet will sound, and the dead will rise again, free from corruption,
and we shall find ourselves changed."
~1 Corinthians 5:51-52
Some Protestant Christians read this quote of Saint Paul's as an explanation of Judgment that is inconsistent with the Catholic Church's doctrine of Purgatory--doesn't he say that our transformation will occur "in a moment, in the twinkling of an eye?" How, then, can the Church teach a purgative state of existence that prolongs entrance into the Kingdom of Heaven?
We must remember that Purgatory exists as a function of our particular judgment (when each soul is judged after death) and not as a function of the Last Judgment (the Second Coming). Saint Paul is describing the transformation of our bodies and the consummation of the created world, not the way souls are cleansed in the period of time up until the Second Coming.
In fact, it is important to remember that Purgatory, by its very nature, has a passing character. After the Last Judgment, there will be no need for Purgatory. Saint Augustine reiterates this point in The City of God: "temporary punishments are suffered by some in this life only, by others after death, by others both now and then; but all of them before that last and strictest judgment."
When the Church professes faith in Purgatory, she does so in regard to the way sins are purified for those who are already assured their salvation in light of their particular judgments upon death. Those who are transformed "in a moment, in the twinkling of an eye" at the end of time will be spared from the experience of bodily death and, in light of their particular judgments will receive purgation through some earthly means, perhaps through the tribulations anticipated at the time of the Second Coming.
The Protestant interpretation of this passage, then, mistakenly applies what Paul describes of the Last Judgment to that of the particular judgment. Purgatory, the existence of which is unmistakably attested to in Sacred Scripture, only applies to the way souls will be cleansed of sin and reconciled with God in the time leading up to the Last Judgment.