God emobodies ultimate power, will, knowledge and ubiquity. As the embodiment of both Caritas et Justitia, no evil can exist in His Presence. People who do evil reject Him. Those who knowingly do evil and thus knowingly reject God cannot enter the Presence of God after the death of the body. So, where can they go, being solely spirit? To the hell of Lucifer.
God made us. We owe him everything, much more than any earthly son owes his father. To take the gift we have been given and then smear it in dirt is a base insult.
For the crime of rebellion, and thus disobedience, angels were sent to Hell. Because we do not have immediate sight of the Presence we have more excuse than the angels. So we get Purgatory for venial sins.
Someone who has willingly and knowingly disobeyed the Commandments cannot then just saunter into Heaven. God will not be mocked. He does not change. He does not deviate. He embodies Justice as well as mercy.
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It is part of the darkness of this era that people, even many Catholics, think that this is not so. In their minds God has gone from being the father of Justice to a sentimental uncle, who will look the other way.