Rev. 21:27 - nothing unclean shall enter heaven. The word “unclean” comes from the Greek word “koinon” which refers to a spiritual corruption. Even the propensity to sin is spiritually corrupt, or considered unclean, and must be purified before entering heaven. It is amazing how many Protestants do not want to believe in purgatory. Purgatory exists because of the mercy of God. If there were no purgatory, this would also likely mean no salvation for most people. God is merciful indeed.