The doctrine of Purgatory is based on the belief that God punishes those who are extremely bad in Hell, and those who are good in Heaven. If a person has been bad all throughout his life, have done every crime he could imagine, and died without repenting for all the evils he had done although he had all the chances of doing it, he is likely a candidate for Hell. But what about a good person who had devoted his life to the service of the poor, but committed homicide because he defended his wife from the rapists? He is not the offended party in this example so he cannot claim self-defense. He did it out of his uncontrolled emotion. Is it not unfair if God should entrust him to the hands of Lucifer? That person had been living a good life. It was only before his death that he killed someone because of his anger. If there is no purgatory and he is not also qualified in Heaven because he killed somebody, where shall he go? It will be against the justice of God to punish eternally in fire a person who repented for his wrongdoings. Hell is for people who do not believe in the mercy and forgiveness of God.
That is why, the theologians of the Catholic Church are absolutely convinced that there should be a place for those who died with sins which could be considered mortal but the committer had expressed repentance of what he did. He cannot be placed in Heaven right away because the Bible said that if a person’s soul is tainted even by a small spot of sin, he is not acceptable to Heaven (Wisdom 7:25; Is. 25:8; Rev. 21:7) He has to undergo first a cleansing which is not an eternal punishment like in Hell. Purgatory is a temporal place of punishment.
To support my points, let me give you the verses in the Bible and read them for yourselves: Numbers 20:12; 2 Kings 12:13; Matthew 12:32; 1 Corinthians 3:11-15.
Let me cite to you the words of a certain Protestant writer in his book, “Is Life Worth Living?” regarding Purgatory. He said, “It is fast becoming recognized that (Purgatory) is the only doctrine that can bring a belief in future rewards and punishments into anything in accordance with our notions of what is just and reasonable. So far from its being a superfluous superstition, it is seen to be just what is demanded at once by reason and morality; and a belief in it is not an intellectual assent only, but a partial harmonizing of the whole moral ideal.”