Because Christ teaches there is a third state of existence after we die, where one can repent of forgiven sins - to repay our temporal debts caused by our sins. Nothing unclean shall enter heaven. I imagine very few will die in an absolute state of grace - through the mercy of God, we can become so, we can throw off all unclean tendencies, all unclean desires, all attachments to anything other than God. It is NOT just about sin! Our will must be turned entirely to God in heaven. Is your will entirely turned towards God now? I doubt it. Purgatory gives us a chance to become even more like Christ.
Regards
Because Christ teaches there is a third state of existence after we die, where one can repent of forgiven sins - to repay our temporal debts caused by our sins
Please direct me to that verse or series of verses in the Word of G-d.
b'shem Y'shua