V Carmen de Beniajan
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Jimmy Akin has presented a logical argument for purgatory. His argument is, as follows:
Premise 1: There will be neither sin nor attachment to sin in heaven.
Premise 2: We (at least most of us) are still sinning and are consequently attached to sin at the end of this life.
Conclusion: Therefore, there must be a period between death and heavenly glory in which the saved are cleansed of sin and their attachment to sin.
In other words, after death those who have achieved eternal salvation but still have some residue or attachment to sin need to undergo purification before entering the joy of heaven. The purification is necessary to achieve the holiness necessary to stand in the presence of God.
To rebut this deductive argument and its conclusion one or both of the premises must be shown to be wrong. That is, to argue against premise 1 one must take the position that sin or attachment of sin is present in heaven. And, to argue against premise 2 one must take the position that sin or attachment of sin does not exist in this life.
Jimmy Akin blogs at Catholic Answers, National Catholic Register, and Jimmy Akin.com.
To Love and Truth 
Food for thought, something my uncle once said to me when I turned my nose up at the idea of deathbed conversions: he said that things probably look at lot different in those last moments of life than they do to us in the trenches, and thus it seems reasonable to him to think there could be such a thing as a genuine change of heart. This is not to undercut your argument about the hold sin has on us, but just to round it out a bit. It made a lot of sense to me.
btw…I also think purgatory makes a lot of sense simply from the argument you use. I just try not to get my brain tied up on it, because I know the best way to shorten/avoid it is to focus on living right, not on whether or not it exists.
Agreed.
Thank you Kathleen. Yes, things are in flux until that moment of death. The converse is, as Paul warns us, also true. Salvation can be lost by a turning away from God.