http://reluctant-messenger.com/reincarnation-pope.htm
I found this particularly interesting.
QUOTE
There was a logical reason why the Emperor was opposed to the concept that all of mankind originally came from God and was returing to God via the cycle of birth and death. Justinian had been convinced by high ranking cardinals that it was not in the interest of the empire to allow Origen's writings to continue to be copied and distributed. A powerful group of Cardinal’s and Bishop’s explained that if every soul had once pre-existed with God, then Christ wasn’t anything special to have come from God. These Cardinals convinced the Emperor that if people realized they were the children of God they might begin to believe they no longer needed an Emperor, or to pay taxes, or to obey the Holy Church. But since they reasoned that only Christ had come from God but God made brand new souls at the time of conception and only the Holy Church could bring these souls to God. Without the protection of the Empire or the guidance of the church, all people would be doomed to be forever cut off from God in Hell. This doctrine was very acceptable to the Emperor. Once Justinian understood the political danger inherent in Origen’s teachings, the rest was simply an Emperor doing what was in his best interest.