Concerning Matthew 25:46, the mistake is in translating “αἰωνιος” as “eternal”.
Having looked the word up in secular and other sources, I have concluded that the best English translation of the adjective is “lasting”. One secular source used it as part of a description of a stone wall. Also, the Jewish historian Josephus, used the word in reference to the length of the prison sentence of a person called “Jonathan”. It has been said that that it was a 3-year sentence… hardly “eternal”. Though the word doesn’t mean “eternal” it sometimes is used in reference to that which is eternal. There is a Greek word, “αἰδιος”, which does mean “eternal”. The word occurs in Romans 1:20 with reference to God’s “eternal power and deity”. If Matthew had understood Jesus to refer to “eternal punishment” and “eternal life” in Matthew 25:46, why did he choose the Greek adjective “αἰωνιος”? Why did he not choose “αἰδιος”?
Besides, the word “κολασις” should not have been translated as “punishment”, but rather as “correction”. The adjectival form of the word was originally used of pruning plants to correct their growth. Later, the word began to be used figuratively in connection with correcting people. Undergoing “eternal correction” does not make sense. How can you undergo the correction process eternally? You would never arrive at the stage where your correction was complete.
As I see it, Matthew 25:46 should be translated like this:
“These [people who would not serve Christ by serving others] will go away into lasting correction, but the righteous into lasting life.”
The word “αἰωνιος” may be used to describe eternal things as well as temporal things. The word itself does not have any inherent meaning of either “eternal” or “temporary”.